Your July 2015 issue Click on title to go directly to the article:

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1 : Your July 2015 issue Click on title to go directly to the article: Monitoring Flooding Black effects Cutworm on corn moth growth arrival and with development Pheromone traps Flooding effects on soybean growth and development Scouting for potato leafhoppers in alfalfa Assessing hail damage to corn and soybeans Sunburn of corn and soybean leaves Scouting for corn rootworm larvae July 2015 Flooding effects on corn growth and development Recent, heavy rainfall has resulted in a few areas experiencing flooding or ponding within fields. Though all crops may be affected, this article focuses on flooding effects on corn. The following comments should be regarded as generalizations. There are many variables that affect how long corn can tolerate flood conditions. When soil is flooded or saturated, there is a limited amount of time before free oxygen is consumed in the soil. When there is little or no oxygen left, corn and other crops do not grow well. Under these conditions, corn roots cannot take up water or nutrients. If water is standing over the leaf tissue, injury to this tissue occurs rapidly. If the corn growing point is submerged or below the soil surface in saturated soils, this growing point may be killed within a few days. Crop injury from flooding or saturated soils occurs more quickly as temperatures rise. This is simply related to the level of biological activity and resulting depletion of oxygen. Damage from flooding or soil saturation tends to occur more slowly under cool conditions. The exception is that, at around 7 C, corn is not growing very fast but pathogens, like Pythium, are still active. Consequently, cool weather is not always positive when field conditions are wet. It is also generally true that tender leaf tissue is more quickly injured than either older tissue or seed that has not yet germinated. A very young corn plant can easily be injured by ponding or flooding, whereas an older plant with toughened leaf and stem tissue might last longer under the same conditions GROWMARK, Inc. The information provided in this letter is general in nature and specific information should be obtained by review of product labels and consultation with the manufacturer. Such information can be materially affected by inaccurate data or assumptions, varying circumstances, known or unknown risks and uncertainties, and many other factors which are beyond the control of GROWMARK, Inc. and results can vary widely. The user will not rely on any information provided herein and GROWMARK, Inc. will not be liable for any reliance on that information. The FS and FS Agronomy logos are trademarks of GROWMARK, Inc. and all trademarks contained herein are the intellectual property of their respective owners.

2 A number of experts will tell us that corn seed is pretty tolerant of flooding or soil saturation as long as the seed coat stays intact. Once the radical or shoot penetrate the seed coat, the developing seedling cannot tolerate more than a few days of excess water. For the emerged corn plant, growth will stop within a couple days following soil saturation or flooding. As soils go anaerobic, the corn seedling will begin to decline rapidly. Under flooded conditions, the corn seedling will be irreversibly damaged within two to three days. Several factors influence the rate and extent of damage from flooding or soil saturation. Temperature is one factor that has already been mentioned. Corn will tolerate flooding a lot longer under cool, than under warm conditions. Water depth is another factor. Although saturated soils are inhospitable for root growth, corn seedlings can tolerate these conditions longer when the leaf tissue is exposed to the air. If the leaf tissue is under water, plant death can occur in less than 48 hours. The only way to accurately assess the situation is to revisit the field(s) often, digging and splitting sample plants to observe plant health. When determining how to manage fields that have been flooded, the hardest decision will relate to the till or notill question. Once saturated soils lose oxygen, they can be slow to regain normal aeration. Tillage can help, but may not be allowed or even practical. Rushing back to replant a saturated field could result in soil compaction or poor stand establishment. Weed control is often compromised by the flooding or soil saturation, so available emergency weed control options should be considered. If the decision is made to replant only ponded or worst parts of fields, be aware that these very late planted areas could become highly prone to insect and plant disease problems. It may be necessary to create an access path into these areas so that timely weed, insect, or disease control can take place. Also, these late planted patches may complicate timing of fungicide or post-emergence herbicide applications because of differences in crop maturity. Flooding effects on soybean growth and development Effects of flooding on soybean health, growth, and development share some similarities with effects on corn and other crops. However, there are some notable differences as well. As with other crops, complete submersion of soybeans will quickly result in irreversible damage or death of the affected plants. In general, under warm conditions, soybean plants can only tolerate about 48 to 96 hours of complete immersion (Dr. Shawn Conley, University of Wisconsin). If the weather is cool and cloudy, and if the soil and water are also cool, survival of soybean plants may be extended. There is a continuum of damage that is difficult to assess until after the fact. It is also important to note whether soybean plants are immersed in clear or muddy water, and whether the water is fresh or is overflow from a pond, slow moving creek, river, or stream. Muddy water seems to be harder on submerged plants and also results in more lasting effects. Fresh, oxygenated water generally permits better survival during immersion. Once the water goes down and exposes the affected soybean plants, make note of whether the plants are covered with mud or are generally clean. Clean plants tend to survive better than mud-coated plants. Wait a few days and then make the first of your detailed assessments. This will involve using a razor blade or sharp knife to split sample plants and buds to observe the relative health of the plant tissue. Regrowth may not yet be occurring, so continued patience is advised. Plants that quickly wilt are not likely to recover.

3 Even after water levels go down and soybean plants are exposed to the air, persistent soil saturation may continue to cause decline of the plants. Or, if plants were never completely submerged but soils have become saturated, the outcome may be similar. Oosterhuis et al, 1990, reported that per cent yield loss occurred with soil saturation during vegetative growth stages, and per cent yield loss occurred with soil saturation during reproductive growth stages. Permanent yield loss often occurs even when the soybean stand visually recovers. Reasons for the yield decline include low gas exchange in the soil, reduced growth of roots and above-ground plant parts, death of root nodules and poor nitrogen fixation, diseases, and general reduction in physiological functions. Workers report that there are notable differences in tolerance to flooding or soil saturation among soybean varieties. Since soybeans often suffer permanent effects from flooding or soil saturation, there may be a stronger urge to replant injured fields or parts of fields. Again, patience is advised. Make the last evaluation of affected fields just before making the replant go/no-go decision. Nothing can happen until the soil is fit for tillage or replanting. If at least partial recovery of the soybeans appears to be likely, it may be preferable to keep the existing stand, rather than going to the cost and effort of replanting, and experiencing the inherently lower yield potential of the replanted soybeans. When determining how to manage fields that have been flooded, the hardest decision will relate to the till or no-till question. Once saturated soils lose oxygen, they can be slow to regain normal aeration. Tillage can help, but may not be allowed or even practical. Rushing back to replant a saturated field could result in soil compaction or poor stand establishment. Weed control is often compromised by the flooding or soil saturation, so available emergency weed control options should be considered. There is nothing certain about survival of soybeans that have been flooded or are growing in saturated soils. If the crop is insured, it may be prudent to allow the adjuster to render an opinion before you get involved. With insured crops, it is reasonable to make the obvious notations about overall appearance of the crop, as well as notes about tissue health and presence of diseases. However, it is usually best to defer to the insurance adjuster on opinions relating to stand survival and yield potential. Scouting for potato leafhoppers in alfalfa June is traditionally the month when we start to detect potato leafhoppers in alfalfa. We anticipate that leafhoppers should soon be found in alfalfa but this does not mean that economic injury is imminent. In alfalfa, leafhopper populations usually don t build up significantly until hot, dry weather sets in. The recent turn toward a summer weather pattern indicates that potato leafhopper scouting season is here.

4 Here s a scouting tip: As long as you are detecting low to moderate populations of adult leafhoppers, only, it is probably not yet time to spray. When you start to detect the leafhopper nymphs, this means that reproduction is occurring and a rapid population increase is near. Insect pests, like potato leafhoppers, that suck the sap of plants seem to prosper under dry or hot and dry conditions. In most cases, this is believed to be because the nutrient concentration in the sap (especially amino acids) is higher and more favourable for insect reproduction. Another reason that these pests seem to prosper when it is dry and/or hot, is because certain beneficial fungi will often hold the insect populations in check. Growth of these beneficial fungi is inhibited during hot, dry weather. There are different potato leafhopper thresholds in use. The following one is fairly simple. Note that a sweep net with 15 inch opening is required for scouting. Take 20 sweeps and average the leafhopper count per sweep. Repeat the sweep sequence in several parts of the field. Note that the following threshold numbers apply to normal alfalfa. An adjustment should be made for glandular haired alfalfa. This is because potato leafhoppers are slow to build up in glandular haired alfalfa varieties and it takes more leafhoppers to cause the same amount of damage as occurs in normal varieties. Be especially watchful with new alfalfa seedings. New seedings can be severely hurt by potato leafhopper feeding. Adult potato leafhopper on alfalfa leaflet Alfalfa height Leafhoppers (inches) per sweep Under to to or taller 2.0 Hopperburn on alfalfa leaves (Left) is a more complicated (and potentially more accurate) threshold table for potato leafhoppers in alfalfa. This table is from PennState University.

5 Assessing hail damage to corn and soybeans Some of the hail damage assessment process is very straight forward and relatively simple, while other parts can be very complex. The following are some guidelines to consider when first visiting hail-damaged fields. A very good resource guide to use in preparation for your field visits is the National Corn Handbook NCH-1 Assessing Hail Damage to Corn. 1. If the crop is insured, it is always best to allow the adjuster to visit the field first. These individuals are generally well trained in hail damage assessment and there is no benefit to risking a different opinion from these experts. 2. Be patient! It will usually take seven to 10 days for enough regrowth to occur to accurately estimate which plants will survive, and to also be able to better observe bruised and diseased tissue. 3. Plan to document everything. A good form to use is the Field Service Call Report Form, available in pads as carbonless forms, and also available as an online, digital document. Take pictures immediately, and over intervals, to use as a record of initial damage and crop recovery. 4. Take your time when evaluating hail damage. The damage usually appears to be much worse than it really is. Tools to have with you: spade sharp knife magnifier measuring tape or measuring wheel flags or stakes to mark individual plants for return visits plastic bags for samples field service-call report forms, pen or pencil camera. (If possible, take pictures in the same place over a period of time to document crop recovery, or lack of.) Minimum information to record: date the damage occurred hybrid or crop variety growth stage of the crop at the time the damage occurred [VERY IMPORTANT] original plant population, recorded from several areas of the field estimated surviving population, documented after a seven to 10 day wait full account of crop protection products applied and when they were applied full account of crop nutrient applications and when the applications were made Comments and tips: Corn, that has been severely damaged by hail up through the V7 growth stage, still has a fairly good chance of survival because the growing point is at or below the soil line. Carefully note hail stone dimples on the soil. Hailstones that sit against plants for a period of time, may cause deep chilling injury.

6 On your first visit, note plants that are in these three categories First: clearly beyond hope; second: questionable; and third: have a good chance for survival. Mark several of the questionable plants for your later visits and follow-up evaluations. Use your sharp knife to carefully split corn plants to examine the growing point. Allow three to five days after the hail event before making this examination. It may take this long for sick and injured tissue to become evident. On soybean plants, note presence of undamaged terminal or axillary buds. Healthy buds will allow the plants to recover. Allow three to five days after the hail event to evaluate bud health on injured soybeans. Effects of bruising and chilling injury often may not be evident for several days or more. Hail injury to soybeans Note: broken stems Variable recovery of hail damaged corn Sunburn of corn and soybean leaves Superficial sunburn of corn or soybean leaves tends to occur with rapid plant growth, rapid initiation of new leaves, and rapid expansion of leaf area. We commonly see sunburn when cloudy or rainy weather is suddenly followed by bright, sunny days. Under these conditions, the leaf surface is often tender and subject to this kind of minor injury. Sunburn is a superficial desiccation of either the upper or lower leaf surface. What we see most often is discoloration of the lower leaf surface, sometimes in patterns that clearly point to solar radiation as the cause. The lower leaf surface may be affected when wind causes the leaf to turn over, or when the lower leaf surface is simply oriented to sunlight. The lower leaf surface is more tender than the upper leaf surface, and more subject to injury. At times, shadow patterns in the sunburn may be evident on the corn leaves or soybean leaflets. With corn, sunburn usually appears to be a silvery discoloration of the leaf epidermis. This can be similar to low temperature injury, although low temperature injury to corn leaves tends to appear on the upper surface of the upper bend of the leaf. Sunburn of corn leaves should not be confused with leaf scorch, which is a much more intense type of leaf injury. Leaf scorch typically shows up in late vegetative or early reproductive growth stages and affects upper leaves under conditions of stress from low moisture levels, low humidity levels, and high amounts of solar radiation.

7 When sunburn occurs to the upper side of the soybean leaf, the leaf takes on a faint bronze or purplish cast. This is sometimes mistaken for Cercospora disease. Cercospora leaf blight does, in fact, predispose soybean leaf tissue to sunburn but a little detective work will help determine whether the sunburn is strictly environmental, or whether Cercospora is helping the symptoms along. With excessive rainfall being experienced in many areas, Cercospora should be considered as one possible cause of the sunburn, although it is somewhat early in the season for Cercospora leaf blight to appear. When the underside of the soybean leaf is affected, we commonly note reddish brown discoloration of veins and a pale reddish or brownish discoloration of interveinal areas. In some cases, the affected area has turned tan or pinkish in color. The reddish veins may be confused with injury from certain ALS herbicides. Sunburn is not believed to affect yield and there is really nothing that can be done about it. In past years, some overzealous individuals have recommended fungicide applications to affected soybeans, believing this to be a fungus disease. Cercopsora leaf blight in soybeans has become increasingly common in many areas, however most of the symptoms observed so far are simple sunburn. Sunburn of corn leaves. Sunburn of underside of the soybean leaf. Bronzing or sunburn of upper side of the soybean leaf. Scouting for corn rootworm larvae Why scout? Both adult and larval forms of corn rootworm can cause significant crop damage. Larvae feed on corn root hairs and roots, and develop through three instar phases before pupating into adult beetles. Larvae rob the plant of valuable water and nutrient flow and put the corn under yield-reducing physiological stress. Feeding sites on the plant are also a common pathway to infection by pathogenic diseases, which can further compromise stalk integrity later in the season. When to scout: Female western and northern corn rootworm beetles lay eggs in the soil in the late summer. The eggs overwinter and begin to hatch when sufficient soil growing degree days have accumulated through the spring. Iowa State University research suggests that 50 per cent egg hatch occurs between accumulated degree days (base 52 F, soil). Rootworm hatch is often thought to coincide on the calendar with lightning bug activity, but this indicator is far less reliable than degree days. Peak hatch normally occurs in June, marking the beginning of the period of time to actively scout for corn rootworms and evaluate their feeding damage.

8 Where to scout:. Scouting larvae can be labour-intensive and costly, so we recommend targeting your scouting activity to those fields which are known to be at greatest risk for infestation. Higher risk fields include corn following corn rotations, fields with high populations of adult beetles the previous August (including previous year soybean fields for variants), weedy fields, hybrids with single corn rootworm traits, and fields with a history of performance issues with either soil insecticides or traits or both. Because adult beetles are mobile, fields adjacent to these areas can also be at risk for rootworms. Aerial imagery collected by UAV can be helpful for identifying field areas with root lodging for targeted scouting. Be aware that corn does not have to be obviously lodging to have serious root damage, so don t be complacent based on good appearance, as you could have a growing problem going undetected. How to scout: Larvae of both western and northern species are very difficult to tell apart. Both are slender white and small (1/2" or 13 mm), with a brown head and a dark tail plate. Dig one plant from each of several representative locations in the field. Dig a 7"x7" cube of soil surrounding the roots and lift the entire plant and root mass out of the ground undisturbed. Gently break away the soil from the root system over black plastic and attempt to visually identify the white rootworm larvae against the black background. Larvae can be difficult to find by hand-sorting soil, and you may have better success immersing the roots and soil in a bucket of water and floating the larvae to the surface. Count the larvae for each plant and average across all plants. Economic thresholds are two (2) larvae per plant with the black plastic method or eight (8) larvae with the wash and float method (Source: Purdue University). If you find threshold numbers of larvae in higher risk fields, expand your sampling net to look at other fields. Unexpected rootworm activity on rootworm-traited hybrids or with insecticides could signal a resistance issue please notify your field sales agronomist in those circumstances. Photo Credit: J. Obermeyer, Purdue University For more information or discussion on any of the topics in this newsletter, please contact your local County Farm Centre FS crop specialist.