INSECTS AND WEEDS IN FOCUS

Transcription

1 INSECTS AND WEEDS IN FOCUS Web site: VOL. XXXIII NO. 6 ENTO/SCS May 20, 2008 T FLEAHOPPERS GENERALLY LOWER THAN LAST SEASON T DECISION MAKING FOR BOLLWORM & TOBACCO BUDWORM T APHIDS ON COTTON WERE SHORT LIVED! T GREENBUGS IN SORGHUM T RICE STINK BUG TREATMENT THRESHOLDS T NEW ECONOMIC INJURY TABLES FOR HEADWORMS ON SORGHUM T TIME TO BEGIN THINKING ABOUT THE SORGHUM MIDGE T WEEDY NOTES T CRAZY ANTS IN THE HOUSTON AREA T NEW INSECTICIDES FOR WHITE GRUB CONTROL T INTERESTING INSECTS T ACTUAL TO HISTORICAL DD60s T EARLY SEASON MAINSTEM NODES AS RELATED TO DD60s T ACCUMULATED HEAT UNITS FOR COTTON IN NUECES COUNTY FLEAHOPPERS GENERALLY LOWER THAN LAST SEASON The cotton fleahopper population remains lower than last season at the same growth stage. There are signs that their numbers are increasing, and plants in the susceptible stage of development need to be monitored closely so that insecticide can be applied in a timely manner as populations exceed 15 per 100 plant terminals. It is not so important to protect every lower plant fruiting site as it is to prevent loss of several fruiting sites up the main stem. As plants increase in size and fruit load into the bloom stage, larger numbers of fleahoppers may be tolerated without yield reduction. When plants are blooming (with exception of the first week of bloom), fleahopper control is rarely justified. During the bloom period base fleahopper treatment on terminal square set percentage. If loss of the tiny squares during bloom approaches or exceeds 50%, fleahopper treatment may be justified. In my experience this amount of loss rarely occurs during bloom. The preceding assumes relatively good earlier square set; that is, prior to bloom. Some of the insecticides for fleahopper include thiamethoxam (Centric), actamiprid (Intruder), acephate (Orthene), and imidacloprid (Trimax). Note that Bidrin is not listed since the new label does not allow for use of the product from squaring until bloom. If you have product with the older label, it can still be used during that growth period. Cotton stage Before bloom After 1 st bloom DECISION MAKING FOR BOLLWORM & TOBACCO BUDWORM Refer to the Extension cotton insect management guide for details with regard to field scouting techniques that are associated with the treatment thresholds listed in the table below. Terminal Inspection Method: Bollworm and tobacco budworm action threshold. Natural Cotton type enemies Non-Bt Bt 15-30% damaged present squares & worms are or absent present present absent** 8-12 small worms per 100 terminals & 5-15% damaged squares/bolls* 4-5 small worms per 100 terminals with eggs present & 5% damaged squares/bolls Use whole plant inspection method Fields that have accumulated 350 DD60s beyond 5 NAWF are no longer susceptible to first or second instar bollworm/tobacco budworm larvae. If two or more key predators are found for each small worm, control measures may not be needed or a microbial insecticide may be considered. *If worm numbers are high, it may not be appropriate to wait until the damage threshold of 5 to 15 percent square damage is reached. **Eliminated by broad-spectrum insecticide application after first bloom. 1

2 APHIDS ON COTTON WERE SHORT LIVED! It is very difficult to watch aphids build up in early season and not react by treating with insecticide as leaves begin to cup and plants which were already looking bad due to high winds look even worse. Here in our Extension cotton we did treat some blocks for cotton aphid, but we did leave several sites untreated. One of the sites not treated happened to contain plots that had good aphid control (seed and granular treatments) along with completely nontreated cotton. The nontreated cotton in the 4 th true leaf stage averaged 70 aphids/plant for about a two week period. These plots could at one time be picked out across the test site, but as aphids began to decline due to predators and parasite activity, plants began to look better. About a week later it was difficult to find the nonteated cotton, but close examination revealed somewhat smaller leaves. Will the infestation make any difference in cotton yield or earliness? I doubt that it will, but yield measurement will be taken. It has been my experience that aphids cause yield reduction if their numbers are high for long periods of time from bloom to near harvest. GREENBUGS IN SORGHUM We have sorghum tests at two locations in the region, but greenbugs are very low at these sites. In our case we would prefer heavy infestation to measure the effectiveness of a number of at-plant insecticide treatments. Reports of greenbugs have been received, but in the cases I know about parasitic wasp and predator activity was so high that treatment was not needed. In our case the small colonies of greenbugs that did occur were rapidly eliminated by the beneficial arthropods. Corn leaf aphids are serving as a site to build beneficial species numbers that should later help with other sorghum pests and then move into cotton. It is dangerous to treat greenbugs on sorghum without just cause as it could set up the crop for additional infestations of several insect species due to destruction of beneficial arthropods. However, if greenbug numbers do reach treatment threshold, delay in treatment could be costly. With the value of sorghum compared to that in the past, fast action will be necessary if the conditions are reached as outlined in the threshold table below. This threshold is the same as in the past, but it should work if more attention is given to quick action once it is deemed necessary. One must be watching the beneficial activity, especially parasitized aphid mummies and predators as they can rapidly reduce greenbug numbers. Once alarmed about the greenbug numbers in a field, wait 48 hours and make another field check to determine if the infestation is still increasing or has begun to decrease. My policy is to never treat for greenbugs, until after a 48 hour reexamination of the situation. Economic threshold levels for greenbug on sorghum at different plant growth stages. Plant size When to treat Emergence to 20% of plants visibly damaged (beginning to about 6 inches yellow), with greenbugs on plants Larger plant Greenbug colonies causing red spotting or to boot yellowing of leaves and before any entire leaves on 20% of plants are killed Boot to heading At death of one functional leaf on 20% of plants Heading to When greenbug numbers are sufficient to hard dough cause death of two normal-sized leaves on 20% of plants Insecticides for greenbug include Furadan, chlorpyrifos (Lorsban, NuFos, and others), dimethoate, and malathion. RICE STINK BUG TREATMENT THRESHOLDS Economic injury level for rice stink bug as number of bugs per acre at the milk stage. NEW ECONOMIC INJURY TABLES FOR HEADWORMS ON SORGHUM Specifically the headworm tables are for the corn earworm, but since we also experience fall armyworm as a headworm on sorghum, the same threshold could generally be used for that species. Very careful attention should be given to the two tables showing the treatment levels since there is very 2

3 good reason the tables are different based on worm size. Note the footnotes to see why there is difference depending upon worm size. Otherwise one is likely to spend entirely too much money on headworm control. Additionaly, I am not comfortable with the large worm economic injury table, although it must be admitted it is based on very solid research. For example, the number of large worms (longer than one half inch) at which treatment is suggested would be about 1 on 5 sorghum heads where the field head numbers were 60,000 per acre, control cost was $10.00/acre, and sorghum value was $8.00/cwt. Table 1. Economic injury level for medium-size (¼ to ½ inch) corn earworm larvae shown as the number of larvae per acre. When the number of larvae per acre exceeds the number in the table at a given cost of control and value of grain per cwt, the value of the protected grain exceeds the cost of control. 1 bloomed do we experience high numbers in the later blooming fields. The exceptions to this observation are when only a few heads begin to bloom in early fields and where large amounts of johnsongrass exist near the early sorghum. In the first situation, within a day or two as more heads bloom the midge become so spread out that they are difficult to find. Once scouting begins for sorghum midge, it must be done daily from about 10 to 11:45 AM. It is okay to scout earlier, but if few midge are found, come back later to see if numbers have increased. See our sorghum publication B-1220 dated 5/07 titled Managing Insect and Mite Pests of Texas Sorghum. For more detail. Find it at publications/results_category.cfm. Use the following table to determine treatment needs for sorghum midge. 1 This table assumes 81% of the medium-size larvae will die in that stage and not contribute to additional yield loss. Table 2. Economic injury level for large (longer than ½ inch) corn earworm larvae shown as the number of larvae per acre. When the number of larvae per acre exceeds the number in the table at a given cost of control and value of grain per cwt, the value of the protected grain exceeds the cost of control. 1 WEEDY NOTES Horse Purslane - Trianthema portulacastrum L. 1 This threshold table assumes all larvae will survive and complete development. TIME TO BEGIN THINKING ABOUT THE SORGHUM MIDGE It will probably be early next month before sorghum midge become a problem. Generally, where sorghum blooms about 3-4 weeks after nearby fields have Synonyms: Sea purslane Plant Habit and Life History: It is a fleshy, succulent prostrate annual up to 2 meters wide and native of the tropics. Vegetative Characteristics: Seedling: Stem pubescent, leaves glabrous, opposite, unequal. Roots: Taproot Stems: Weakly diffusely branched stems are 3

4 erect early but later prostrate up to 2 meters long. Leaves: Bright fleshy green, subopposite to opposite, widely elliptic to nearly orbicular 1.5 centimeters long; petioles 1-2 centimeters long; stipules free at apex. Pairs are unequal in size. Special Identifying Features: Leaves opposite and in pairs of unequal size. Flowers pink to rose purple. Distribution: Ranging from Florida to Texas and California, north to New Jersey, Missouri and Oklahoma. NEW INSECTICIDE FOR WHITE GRUB CONTROL DuPont has a new insecticide (Acelepryn) labeled for white grubs and several other pests infesting landscape and recreational turfgrass. The label includes golf courses as well as landscape ornamentals, interior plantscapes and sod farms. The product is a new insecticide class with novel mode of action. In our region the best time to evaluate whether treatment for white grubs is necessary is around July 4. By that date all eggs have hatched, grubs can be counted, significant damage has not been done, and control is easier to achieve. The challenge will be to get the material into the soil and not have it deposited on the grass and thatch. INTERESTING INSECTS Do you realize there is an entire discipline in entomology devoted to the study of resistance of crop plants to insects. In recent years that study has increased dramatically due to the genetic engineering revolution of which we are still in the model T days compared to what will occur in the future. There is a movement in some circles to eliminate or greatly slow the genetic engineering revolution, but that is not going to happen. CRAZY ANTS IN THE HOUSTON AREA The crazy rasberry ant (suspected species) is an invasive species found several years ago in the Houston area. It causes many problems due to the very high numbers encountered in homes, automobiles, buildings, and other places. This ant often causes great annoyance primarily due to their great numbers. The ant does not have a stinger, but they can bite, causing a relatively sharp but quickly fading pain. Even though the ant can bite, it does not seem to be an aggressive biter. The ant is very difficult to control. It has been suggested that Termidor (perimeter treatment), Top Choice (lawns), and Phantom (inside baseboards) be used by homeowners. Even before the new technology came along there was much activity dealing with insect resistant crop plants. For example, when I was in school one of our text books published in 1951 was titled Insect Resistance in Crop Plants. We studied such areas as factors that affect the expression or performance of resistance, methods and problems in breeding for resistance, and specific examples in a number of cultivated crops. There was also a special course in host plant resistance which is still being taught. For more information on the crazy rasberry ant go to the website: tamu.edu/ants/exotic_tx.cfm. 4

5 ACTUAL TO HISTORICAL DD60s The chart below compares the actual (2008) to historical DD60s ratio for cotton from 3/15 to 5/15. The value of 1 represents the historical average. The first 30 days of growing conditions were prone to cycles of above or below average DD60s accumulation. During the last 30 day period (4/15-5/15), DD60s have accumulated close to the historical average with the exception of a couple of cooler than normal periods. Actual to Historical DD60s Ratio =hist. avg /15 3/22 3/29 4/5 4/12 4/19 4/26 5/3 5/10 EARLY SEASON MAINSTEM NODES AS RELATED TO DD60s Early in the season, a new node or branch will develop at a rate of approximately one every 50 DD60s, or one very 2.5 to 3 days during warm weather. As the season progresses or shortly after first bloom carbohydrates are diverted to bolls and the same linear rate of node develop does not hold true. As the boll demand increases, the level of photosynthate or carbohydrate in the reserve tank decreases, and falls below the level for continued vegetative growth. This is the normal progression, except when boll retention and development are below normal due to insect damage or poor weather. When cut-out (NAWF=5) approaches, the rate of new node production decreases dramatically and finally ceases. Early season mainstem nodes as related to DD60s n o d e 10 n u 8 m 6 b 4 e 2 r 0 emergence DD60s 5

6 ACCUMULATED HEAT UNITS FOR COTTON IN NUECES COUNTY Listed below are the accumulated heat units for cotton for March, April, and the first two weeks in May. Daily heat units or DD60s can be calculated by using the following method: DD60s = [(Daily Max. Temp. + Daily Min. Temp.)/2]-60. Accumulated heat units for cotton, Nueces County, Texas AgriLife Research and Extension Center, Corpus Christi, 3/1-5/15. 3/1/2008 DD /1/2008 DD /1/2008 DD /2/ /2/ /2/ /3/ /3/ /3/ /4/ /4/ /4/ /5/ /5/ /5/ /6/ /6/ /6/ /7/ /7/ /7/ /8/ /8/ /8/ /9/ /9/ /9/ /10/ /10/ /10/ /11/ /11/ /11/ /12/ /12/ /12/ /13/ /13/ /13/ /14/ /14/ /14/ /15/ /15/ /15/ /16/ /16/ Total /17/ /17/ /18/ /18/ /19/ /19/ /20/ /20/ /21/ /21/ /22/ /22/ /23/ /23/ /24/ /24/ /25/ /25/ /26/ /26/ /27/ /27/ /28/ /28/ /29/ /29/ /30/ /30/ /31/ Source: cwp.tamu.edu For more information contact: Roy D. Parker Extension Entomologist rd-parker@tamu.edu Dan D. Fromme Extension Agronomist d-fromme@tamu.edu State Hwy 44, Corpus Christi, TX (361) , Fax (361) View our newsletter earlier on the internet at Also pest management information is available at *********************************************************************************************************************************************************** Educational programs conducted by Texas AgriLife Extension serve people of all ages regardless of socioeconomic level, race, color, sex, religion, handicap or national origin. The information given herein is for educational purposes only. References to commercial products or trade names is made with the understanding that no discrimination is intended and no endorsement by Texas AgriLife Extension is implied. The Texas A&M University System, U.S. Department of Agriculture, and the Commissioners Courts of Texas Cooperating