Weed Management, presented by Jon Carpenter, Nevada Department of Agriculture, at the Nevada Landscape Association Conference and Trade Show,

Transcription

1 Weed Management, presented by Jon Carpenter, Nevada Department of Agriculture, at the Nevada Landscape Association Conference and Trade Show, February 17,

2 What is a weed? Simply put, a weed is a plant that is growing out of place. An extreme example is roses growing in a corn field. More realistic and common examples of plants growing out of place are common dandelions growing in a lawn, or grass taking over a flowerbed. Weeds become problems in agricultural fields, ornamental and aquatic sites, and rights of way. 2

3 Many of our hard to kill weeds are considered invasive. Most invasive weed species did not evolve here in North America. They are exotic species that came from another continent. They were transferred here through human activities: as weed seed in feed, as weed seed in crop seed, in livestock animals and their manure, brought as ornamental seed, roots or shoots, etc. Generally, this transportation happened in the last 200 years, when transportation became fast and efficient. These introduced, exotic species out-compete native plants, taking over environments once held by the native plants. In some cases, when the exotic plants out-compete the native plants, they are removing the food source for native animals. Weeds such as perennial pepperweed or Canadian thistle can restrict access to streams, thereby adversely effecting recreation. 3

4 In the last 200 years, some plants imported for the horticultural trade have escaped and naturalized in our ecosystem. A good example of this phenomena is purple loosestrife, a very pretty plant. It was originally imported as an ornamental plant, but has turned out to be very aggressive, out-competing native riparian plants. It will create a mono-culture. Purple loosestrife is capable of out competing most of the original vegetation growing along a stream bank or in a riparian area. Soon, all that is growing there is purple loosestrife. Purple loosestrife is not as effective as the native plants in stabilizing the stream bank and reducing or controlling erosion. The end result of a purple loosestrife invasion is a loss of wildlife habitat and degradation of the stream or riparian area. Contaminated shipments of soil and water are another common way that invasive plants spread. Historically, some weed seeds were brought in the soil used for ballast in ships. Weeds or their seeds can be introduced through weed or seed contaminated water, soil, seed, feed, crops or plants. 4

5 Some plants have certain attributes that lend them to being good landscape plants. Pretty plants that are easy to grow like purple loosestrife and toadflax, also known as butter and eggs, are two good examples. These plants were likely introduced by the ornamental plant industry and have become serious noxious weed problems. Some aquatic plants are easy to grow, which is why the aquatic ornamental plant industry imports and sells them. Unfortunately, they are sometimes flushed with the fish out of aquariums or are transported from ponds by flowing water, wildlife, or through recreational activities like boating. These aquatic plants can rapidly grow and spread throughout the water body and into new ones where they may outcompete the native plants and can become a serious weed problem. Eurasian watermilfoil is a good example of this phenomena. It was probably intentionally introduced and first documented in the early 1940s on the East Coast of the U.S. It now infests the waters of Lake Tahoe where intensive harvesting and prevention is used to manage the plant. 5

6 Noxious weeds are those that, due to their negative impacts, society has determined that we are legally responsible for managing. What does this designation really mean? It means that government entities are responsible for removing it on public lands and property owners are legally responsible for removing it from private lands. If a private property owner does not remove it, the government can come onto your property, remove the noxious weeds, and charge you for the removal. Property owners are legally responsible for removing noxious weeds from their property and preventing the spread of the noxious weed to adjacent properties. 6

7 Weeds create many negative impacts: Weeds displace native plants and other desirable vegetation. This removes habitat and food sources for desirable animals, both wild and domestic. Weeds can create a monoculture. Because these plants are so competitive, they will soon be the only species of plant growing at some invasion sites. This creates an area with little biodiversity. Few animals feed on or use the weeds for cover or nesting sites. Weeds will negatively impact recreation areas, making it impossible to get to water bodies or other recreational sites. Additionally, many of these plants have stickers, thorns, burrs, annoying odors or other characteristics that prevent or interfere with the enjoyment of recreational sites. 7

8 Weeds can take over rangelands, displacing forage plants needed for range animals, both wild and domestic. As the health of the rangeland plummets, the capability of the rangeland plummets and so does the property value of the rangeland. Weeds can hasten the extinction of endangered species by out-competing the endangered species plants and taking over their habitat. They can hasten the end for endangered species animals by taking over their habitat and/or removing their food source. Weeds can increase soil erosion, since many weeds do not hold the soil in place and do not stabilize the stream banks. 8

9 Weeds can impede the flow of water. The water can not flow due to the volume of aquatic weeds in the channel. Weeds can seriously affect water quality. As mentioned before, weeds are not always good choices for controlling erosion. Increased erosion increases the sediment load in the water, affecting water quality. Phosphorus will attach to sediment particles, so increased sediment can increase phosphorus pollution in waterways. Increased weeds in the waterway can lead to increased die off when water levels drop. The decaying vegetation can cause odor problems. Weed infestations can have an affect on the aesthetic value of land and waterways, making them less attractive. The loss of aesthetic value equates to a loss of monetary value. Weeds can affect the water-holding capacity of water bodies. Aquatic weeds trap sediment, which in turn decreases the water volume capacity of reservoirs, channels and other water bodies. 9

10 Weeds may have an adverse affect human health. For example, the potential for West Nile Virus can increase due to aquatic weed infestation. An infestation of either a floating aquatic weed or a shoreline weed can enhance mosquito larva habitat. The weeds may offer the larva protection from predators. The weeds may also interfere with the application of a larvacide, preventing the pesticide from getting into the water and to the larva. 10

11 Our most serious weeds are superior competitors. They compete for water, nutrients and light with the native vegetation. These are plants that did not evolve in their present location. They were introduced, generally from another continent. As a result, they have few natural enemies. They do not have animals, insects or diseases that prey on them and keep them in check, as they do in their native habitat. This makes them superior competitors. 11

12 This is a perennial pepperweed or tall white top infestation on the Truckee River near the Tracy Power Plant. The perennial pepperweed has out-competed whatever native vegetation was originally present, creating a monoculture. This area provides no cover, nesting or food for wildlife. It impedes access to the river at this site. It does not control erosion of the streambank as well as the native vegetation does. It degrades the river and decreases the value of the land. 12

13 There are many ways to classify weeds. In our area, one of the most basic distinctions is whether the weeds are aquatic or terrestrial. t This distinction affects the types of herbicides id you can apply and, in many cases, the method of application you can use. Terrestrial weeds include some thistles, cheatgrass, perennial pepperweed and the knapweeds. Not every thistle is considered a weed. There are many thistles that are actually native and provide food and habitat for animals and insects. This is why proper identification of the plant that you wish to control is important. Invasive weeds destroy rangeland habitat, decrease land values, and impact recreation. Aquatic weeds include Eurasian watermilfoil and dnaiad, which hgrow in the water. Purple loosestrife, perennial pepperweed, cattail, and bull rush grow on the banks of water bodies or in very shallow water. In our area, the most abundant aquatic weeds are those that grow on the bank or in very shallow water. The largest aquatic weed problem is caused by noxious weeds that grow on the banks or shores of water bodies, not in the water itself. Lake Tahoe has a significant Eurasian watermilfoil infestation. Currently, local authorities don t allow the use of aquatic herbicides in the lake. Control measures include mechanical removal and prevention. Unfortunately, mechanical removal breaks up the Eurasian watermilfoil into small fragments and each fragment can grow a new plant. Educational efforts are underway to reduce the spread to other portions of the lake by careful inspection of boats and boat trailers before and after launch. Herbicide labeling will tell you if the product is registered for use in aquatic sites. If a pesticide is not approved for aquatic applications the label will say do not apply directly to water or do not allow the pesticide to drift into water. 13

14 The aquatic weeds are divided up into two broad categories. The vascular plants have a system that transports water and nutrients throughout the plant. Vascular plants have roots, stems, leaves, and flowers. Algae do not have roots, stems, leaves or flowers. 14

15 There are four basic categories of flowering (vascular) plants: Submersed plants are rooted in the soil and produce some small flowers on the waters surface. Examples of this type of plant are elodea and Eurasian watermilfoil. Rooted floating plants are rooted with some leaves and large flowers on the water surface. An example of this type of plant is a waterlily. Free floating plants are not rooted in the soil, they get nutrients t directly from the water. These plants are usually very small and have leaves and flowers on the water surface. Duckweed is an example of this type of plant. Emergent plants grow in shallow water and often on the bank. Examples of this type of plant include cattail and purple loosestrife. 15

16 Microscopic algae give water a split pea soup appearance. Filamentous algae form dense mats and may be called moss or slime or even pond scum. Chara has a brittle texture and may be confused with flowering plants. 16

17 Plant growth can be broken down into four stages: Seedling: Seed germinates and plant begins to grow. This is the best stage to control a weed plant. They are easy to remove using mechanical means at this stage. They are easier to control by chemical means at this stage. They are small, the leaves and roots are tender, and you can use less chemicals to get control. Vegetative: Stems and leaves grow Reproductive: Flowers form, are pollinated and seed forms Death or dormancy: Plant dies or goes dormant for the winter 17

18 Plants can also be classified by their life cycle. An annual plant has the four stages of growth discussed earlier, seedling, vegetative, reproductive and death, but all four stages occur within one year, hence the name annual. A biennial plant goes through the same four life stages in a period of two years, with seedling and vegetative growth the first year and flowering, seed formation and death the next year. 18

19 The third life cycle for plants is perennial. Perennial plants live three or more years. These plants have the same four stages of life, but they go dormant rather than die. These plants can spread by root growth, rhizomes (underground stems) and/or seed production. Obviously, a plant that can reproduce itself by so many methods will be very competitive. Most noxious, invasive weeds are perennial plants. Regardless of the life cycle, control is best achieved during the seedling stage. 19

20 As far as managing weeds goes, the best approach is integrated weed management. Integrated weed management looks at the weeds involved and the severity of the infestation, then looks at all the control methods available to combat the weed infestation. The first step in weed control, as with any pest, is to identify the weed. When you have identified the weed and its life cycle, you can then identify the best biological, mechanical and chemical controls for that particular weed. 20

21 Prevention, by using only certified weed-free seed, is an good start. Using weedfree straw or mulch and fully composted manure or plant materials is another way to prevent weed spread or introduction. Accepting FREE fill dirt and partially composted manure may well cost you more in the long run than buying good quality products in the first place, if you then have the expense of controlling noxious weeds! Preventative methods for aquatic weeds include inspection of water craft before they are allowed to be moved from infested waters. Watercraft and trailers should be thoroughly inspected and cleaned before leaving a site that is known to be infested with aquatic weed species, such as Eurasian watermilfoil. Mechanical control, by pulling or digging up the weeds, is a very effective control method for small infestations. Burning can be a good control method for certain weeds, but comes with its own set of potential problems, including wildfire. 21

22 Herbicides are not the only option for weed control. Biological control, using insects or animals to help control the weeds, can be part of a weed control plan. Generally, the results are not immediate and may not even occur in your lifetime. Again, you must first identify the weeds to make sure the animal or insect will eat it. In most cases, if you are introducing a new species, for example, grass carp, you will need a permit. In Nevada, permits for grass carp may be obtained from the Nevada Department of Wildlife. Using animals to graze the weeds as a first pass and then spraying weed re-growth can be a effective approach to reducing the infestation of some weeds. Again, this can be labor intensive and will not work in all areas. It can be difficult to confine the grazing animals to just the weed infestation and keep them away from desirable plants. There are some weeds and some large infestations that are best controlled or reduced with chemical means. 22

23 There are many herbicides available. Again, it can not be emphasized enough, you must identify the weed before you can determine a control method. Identification is also important when determining a chemical control method. Herbicides can be broken down into two main groups, based on how they kill plants: contact and systemic. Contact herbicides must contact the plant and the plant must be actively growing for the herbicide to be effective. They kill the part of the plant they touch, but do not move any further in the plant. They are very gratifying, because you see the effect fairly quickly. They are good for controlling annual weeds but they are not good for controlling perennial weeds, because they only kill the part of the plant they touch. Systemic herbicides work slower but they translocate in the plant, that is they move into the plant tissues and move throughout the plant. They do not kill just the part of the plant they touch, but will move throughout the plant, killing even the roots. This is an important if you are controlling perennial weeds. 23

24 Another way herbicides are divided is by what they kill: selective versus nonselective. Selective herbicides are more toxic to a specific species or group of plants. The most basic division here is grass or monocot plants versus broadleaf or dicot plants. Selective herbicides will kill one group or the other. 2,4D, a broadleaf plant herbicide, is a good example of one of these types of herbicides. Non selective herbicides are toxic to a broad range of plants. These herbicides will kill grass and broadleaf plants. A good example of this type of herbicide is Roundup or glyphosate. In order to do effective weed control with herbicides you must first identify the weed. You must also determine the site where the weed is growing. The herbicide your choose should be labeled to control that weed and to be used on that site. Sites includes such designations as rights of ways, croplands, pastures, riparian areas, etc. If the herbicide is to be applied to a specific crop, the crop should be listed on the label. For example, if the site you wish to apply herbicides on is a field of alfalfa, then alfalfa must be listed on the label as a site or crop safe for application of that particular herbicide. If the weed is growing in a pasture then pastures must be listed on the product label as an approved site, and so on. 24

25 Another important consideration for pesticide application is managing drift. Drift is the movement of a pesticide through the air during the time of application to a site other than that intended. In other words, you were spraying weeds and the pesticide drifted over and hit non-targeted plants. If you are applying pesticides for plants or insects, you need to think about drift and how to prevent it. If you are applying a pesticide and drift occurs, it is a label violation and you may be held liable for damages to non target crops as well as other items. An example of non target damage is when you are applying an herbicide to control weeds in a pasture and the herbicide drifts onto a nearby garden and ornamental landscape causing damage. How do you control or reduce the potential for drift? 25

26 Use coarse spray ( microns). Bigger droplets will not travel as far as fine droplets. Avoid windy and gusty conditions. Almost all restricted use pesticides (RUPs) and over-the-counter pesticides come with this warning. Use buffer zones. A buffer zone is an area where you don t apply pesticides that is generally between the target area and the adjacent non target area. Leaving the buffer zone untreated prevents drift onto a sensitive non target area. Drift retardants or thickeners can be added to the pesticide before application to help reduce the potential for drift. Talk to your supplier regarding the best drift retardant to add to your specific pesticide. Avoid high temperatures. Generally, high temperatures are those greater than 85 degrees F. Almost all restricted use pesticides and over-the-counter pesticides come with a warning not to use the product at high temperatures. Most pesticides will volatilize if they are applied during periods of high temperatures. This means the pesticide goes from a liquid to a vapor. The vapor may drift to non target sites, damaging non target plants or animals. Herbicides have the most potential for crop damage 26

27 Many times, weed management consists of preventing the weed from spreading. For annual and biennial weeds, the best way to prevent spread is to prevent seed production. For perennial weeds, reproduction can be both seed production and vegetative reproduction. For all three life cycles, seed production can be manually controlled by removing the seed heads in a small infestation. For larger infestations, pesticide applications may be required. 27

28 Pesticide application timing is dependent on the life cycle of the weed. Again, this is one of the many reasons it is so important to identify the weed before deciding on the control method. For annuals and biennials, the best times to control are at the seedling stage and before seed production. At the seedling stage, the plant is not that robust or that large. It will take less herbicide to kill the plant. Since annuals and biennials produce via seed, destroying them before they produce seed will help reduce or eliminate an infestation next year. For perennials, pesticide application timing depends on the species. Remember that control of perennial weeds is controlling not only seed production, but controlling the root system. 28

29 There are many barriers to pesticide uptake by plants. The leaf cuticle is the waxy substance that is on the leaves of plants. The cuticle helps keep water in, so in our arid climate, many plants produce heavy leaf cuticle. Unfortunately, the leaf cuticle can also interfere with herbicide uptake by the leaves. Leaf hairs are another adaptation that plants have that can interfere with pesticide uptake. The pesticide will actually sit on the plant hairs and not touch the leaves. The pesticide will evaporate or volatilize from the leaf hairs and never be absorbed by the leaf itself. 29

30 Environmental conditions play an important part in the timing of pesticide application. Obviously, applying pesticides when rain is expected is not a good idea. The pesticide will wash off the plants. At best, you have wasted money and at worst you have damaged non target plants with the rain water runoff! Applying pesticides under windy conditions can also be a waste of time and money. Similarly, the wind may carry the pesticide to non target plants, animals and areas. This can cause problems for you, not the least of which are lawsuits and monetary penalties. Applying pesticides during extremes in temperatures is never a good idea. If the temperature is too warm, the pesticide may volatilize or evaporate before plant uptake can occur. Additionally, many plants shut down during hot temperatures. Most pesticides work on actively growing g plants. If pesticides are applied when the plants are dormant, little to no foliar uptake will occur. Similarly, during cold weather the plants are not really actively growing and plant uptake may not occur. In both cases, you have wasted time and money applying the pesticide and may have caused damage by both non target application of the pesticide and an increased likelihood of pesticide pollution. Periods of higher humidity are a great time to apply pesticides, but we don t often get humid conditions here in northern Nevada. Humidity is generally higher in the early morning. Winds are generally calm in the morning. In the summer, the temperature is generally low in the morning. If there is no chance of rain, early morning is a good time to apply pesticides in the summer. 30

31 Again, as stated before, pesticide application results will be poor if you apply before or during a rain storm, when winds are high, or during extremes of temperature. The effectiveness of the pesticides are reduced under high or low temperatures. 31

32 The site of the application must be listed on the label. If you apply pesticide to an area or location not listed on the label, you may do crop damage, it is a label violation,and you can be fined. Some example of sites are non crop, right of way, specific crops, aquatic sites, etc. When you are applying pesticides you must always have the labeling with you. 32

33 What happens to the herbicides that are applied? What you as a pesticide applicator want is to apply the herbicide to the weeds, have it be absorbed by the weeds and then the weeds die. Many herbicides are intercepted and absorbed by plants. But some of the herbicides break down on the leaf surface due to sunlight, temperature or microbes. Some of the herbicide comes in contact with the ground and breaks down in the soil. Some herbicides bind to soil particles and don t leach into groundwater. Some remain in the soil and are leached by water, moving into the groundwater system. 33

34 Many herbicides have the ability to leach into the groundwater. The first four products on the list above, atrazine, simazine, diuron, and prometon, have been found in the groundwater of Nevada. 34

35 Some examples of a right of way includes utility lines and easements, roadsides, and railroads. Right of way herbicide applications are mostly about safety including: fire prevention, improve visibility, or prevent damage by roots. In some cases, you are trying to improve aesthetics. 35

36 Right of way weed control requires an integrated approach, like all other weed management. Mechanical control can provide short term results. This would include mowing or burning. Preventative measures, by not introducing the problem in the first place, and biological controls would depend on the weed species. Chemical controls are used, but in right of way pesticide applications, you must be very aware of the adjacent land uses. Many right of way areas are adjacent to crop lands, grazing lands, or water ways. Many of the pesticides used in right of way weed control are also used on crop lands or rangelands. Care must be taken to prevent drift. Care must also be taken to prevent surface water or groundwater pollution. 36

37 Pre-emergent weed control can be a very effective method for weed reduction and prevention. Pre-emergent herbicides work in the soil, killing plants as the seed germinates. They are applied in spring or fall and must be incorporated into the soil. This is usually accomplished by precipitation or sprinkler irrigation. In general, preemergent herbicides don t bind to soil particles and therefore are capable of leaching into groundwater. Pre-emergent herbicides are the most common pesticide contaminants found in groundwater in Nevada. 37

38 Many factors can contribute to groundwater contamination: Bigger soil particles like sand are more likely to allow herbicides and other pesticides to leach. Areas of high precipitation and irrigation are more prone to groundwater contamination by herbicides and other pesticides. Areas where groundwater tables are near the land surface are also more likely to be contaminated t by pesticides. id 38

39 Effective weed control requires that you first identify the plant that you wish to control. For help identifying weeds, the books Weeds of the West and Aquatic and Riparian Weeds of the West are very helpful. There are several computer programs that can help identify weeds. There are also weed specialists at both the Nevada Department of Agriculture and the University of Nevada Cooperative Extension that can help you identify your weeds. With any pest control you do, you must make sure you know what species you are dealing with: what plant, what insect, what animal. 39

40 The next few slides will give a brief overview of some common weeds in Nevada. Scotch thistle is a common weed in our area. It is a biennial, dry land weed. It reproduces by seed. It is much easier to control during the first year of growth than in the second season of growth, as shown in the picture. It can be controlled by mechanical means, by chemical means and by biological means (grazing). It has a large seed bank in the soil and will sprout when conditions are right. 40

41 Perennial pepperweed is a perennial, as the name implies. It occurs in both riparian and dry land settings. It requires water to germinate and become established the first year, but then it is quite drought tolerant. It is a very invasive noxious weed that reproduces by both seed production and by vegetative reproduction. This plant is so adept at vegetative reproduction that even a very small piece of root will generate a new plant. During flooding or other disturbances, small pieces of root are transported, deposited and a whole new infestation of perennial pepperweed can begin. While perennial pepperweed is certainly considered a terrestrial weed it often grows very close to waterways. This will have a direct effect on the herbicide that you use to control this weed. Because the product you use may drift into water you must select an herbicide that is allowed for aquatic sites. 41

42 Perennial pepperweed is difficult to control. Mechanical removal methods will work on very small sites or infestations. It will require more than one season or session of mechanical pulling. Disking or ripping will not work as a control method. Disking a perennial pepperweed infestation will make the infestation worse, as each small piece of root will generate a new plant! Herbicides will work on perennial pepperweed, but you will probably need more than one application and will need to monitor for several seasons afterwards. This is due to the seed bank that perennial pepperweed can produce after just one season. You must also use caution on wet sites. Many perennial pepperweed infestations are on the banks or shores of water bodies. The herbicide must be labeled for aquatic site use in these areas. If it gets into the water and it is not labeled for use at aquatic sites, it may damage unintended plants and animals. It would also be a pesticide label violation. 42

43 Eurasian watermilfoil is a perennial, submersed, aquatic weed. Control of this weed is problematic in our area. It can be controlled by herbicides that are labeled for water use, but herbicides are not allowed at Lake Tahoe. It primarily reproduces vegetatively, with small bits of plant generating whole new plants. The small bits of plant can be produced by waterfowl or by human activities, such as boat propellers, jet skis, etc. It can also be transferred by boat trailers and other devices to different areas on the lake or to different water bodies. Integrated control measures include prevention by inspection of water craft and herbicide treatments. 43

44 One method that is used for managing Eurasian watermilfoil is harvesting. Harvesting or mechanical removal is also used for other aquatic weed species. It is very expensive and requires specialized equipment. It provides quick results. The harvested weeds are transported to a landfill. There can be a problem with weed spread during the harvesting and transport process. 44

45 Salt cedar or tamarisk is a perennial tree or shrub introduced by the United States government as a soil stabilizer. It is originally from China. It is very invasive, growing on both in both dry land and in riparian (near a water body) settings. 45

46 Salt cedar will actually change the environment around itself by absorbing salts and depositing the salts in its leaves. When the leaves drop, the salt is added to the soil, making it inhospitable for other plants to grow and thrive. In this way, salt cedar will create a monoculture. 46

47 Salt Cedar can not be managed by most mechanical means. It will readily resprout after cutting, mowing, chaining, burning or plowing. There is some evidence that flooding for a period of one to two years is effective in destroying a stand of salt cedar. Flooding for that period of time is difficult to maintain here in the arid west. Chemical controls are either on cut stump (most common) or a foliar (leaf) application. Triclopyr (Garlon ), imazapyr (Arsenal ), or glyphosate (Roundup or Rodeo ) may be effective at eliminating salt cedar. Make sure to use a waterlabeled formulation near water. 47

48 A beetle, Diorhabda elongata, has been introduced in some areas of Nevada to combat salt cedar. As with all biological controls, results from this insect introduction are slow and must be measured over time. 48

49 In conclusion, the steps for weed management are: Identify the weed. Identify all the control methods available for controlling that weed. Identify the control methods most useful and useable (site specific) for your infestation in your situation. Monitor your results and modify your management plan as necessary. 49