Virginia cotton requires a thrips control product at planting to preserve yield and avoid maturity delays. This is especially true since the arrival of tarnished plant bugs. Any maturity delay early-season will likely magnify plant bug injury. Cotton planted at the end of April and first week of May has put on 1-2 true leaves. It is time to scout for thrips injury and make foliar applications when necessary.
Levels of injury to cotton seedlings rated from ‘0’ (no damage) to ‘5’ (dead terminal
or plant) from thrips. Injury at ‘2-3’ or above approximates a threshold for intervention with an
insecticide application. (Photo and caption from Kerns et al., 2018)
Using a seed treatment alone will likely require a foliar spray based on research from the Tidewater AREC. In-furrow aldicarb and in-furrow imidacloprid with a seed treatment should not need a foliar spray. Scout cotton planted with in-furrow imidacloprid alone and determine if a foliar application is necessary (often it is not – saving you time and money).
All cotton planted in Virginia is under high risk for thrips injury. NCSU prediction model shows risk increasing in later-planted cotton. This model was highly accurate in 2018.
Tips for foliar applications: Consider plant-date and growing conditions. Cotton planted late-May into warm soil may not need a foliar spray. Do not apply foliar acephate if plants are growing fast with no to minimal thrips injury. Thrips injury is likely for all cotton planted in Virginia and risk will be high until plants are no longer susceptible. The three diagrams below from the NCSU model show when seedling susceptibility declines based on planting date (May 1, May 8, May 15). The blue line on these diagrams shows you when risk for thrips injury is highest.
Spraying is most effective when the first leaf is the size of a pencil tip to a mouse ear. I recommend a 6-8 oz. rate of acephate. Several scenarios may be responsible for reduced efficacy of sprays:
1. Rain. Acephate is not a rain fast product. Consider reapplying if necessary.
2. Resistance. Acephate at 3 oz. per acre has become less effective in spray tests. Rotate to Radiant if another spray is required or use a higher rate.
3. Species composition. Tobacco thrips are most common in VA, but western flower thrips can co-infest. Acephate is less effective on this species. Rotate to Radiant if another spray is required.
As always, call/text/email me with any questions. Good luck and happy planting!
Large aphids populations have been observed in alfalfa this year following insecticide applications targeting alfalfa weevil. If you haven’t scouted for alfalfa weevil in Virginia, you should. See the bottom of this post for a weevil summary.
Aphids, typically pea aphids, can be problematic when their natural enemies are disturbed. They can reduce vigor and cause wilting in first cuttings. If early cutting is not an option, several insecticides (mostly pyrethroids) are labeled for their control. Low label rates are generally effective as long as you ensure good coverage. Scout for aphids by pulling 30 random stems per field and counting the number of aphids. This guide from Iowa State can help you make treatment decisions.
Most of the aphids I have seen in Virginia alfalfa are pea aphids (left) and cowpea (right). If you think you have another species, please give me a call or send an email.
Photos Erin Hodgson, Iowa State
My thanks to Lane Grow from Southern State Cooperative for his ongoing efforts to scout and report problems in western Virginia.
Alfalfa weevil information
Scout fields by pulling 30 random stems and inspecting foliage for weevils. Weevil larvae are small, can be white, yellow, or green, and have black heads. They are often tucked tight into new growth. It’s possible to dislodge larger larvae so be careful or collect stems into some container that catches these. I use a plastic freezer bag and insect stems in the shop or truck. This guide from Penn State can help you make spray decisions. Cutting alfalfa is an option if you don’t want to use pesticides. I recommend using clorpyrifos based on spray tests in 2018 and 2019. Some people have been successful with indoxacarb (Steward) or pyrethroids (many brand-name and generic options). Coverage is essential with any product.
Please see the attached table for current black light trap captures of corn earworm moths: BLT_6_Sep_2018
Average nightly captures of corn earworm moths in local black light traps this week were: Hanover=1.0; Southampton=0.7; Suffolk=28.1; Warsaw=3.6; Waverly=3.7. Here is the table: BLT_30_Aug_18
Average nightly corn earworm moth captures for local black light traps this week were as follows: Chesapeake=8.0; Dinwiddie=42.6; Hanover=3.4; Isle of Wight=0.9; Prince George (Templeton)=1.3; Prince George (Disputanta)=3.3; Warsaw=6.6; Southampton=0.9; Suffolk=33.0; and Sussex=1.9
Here is the link to the data table: BLT_23_Aug_2018
Thanks to Watson Lawrence, Mike Parrish, Laura Maxey Nay, Livvy Preisser, Scott Reiter, Mary Beahm, Neil Clark, and Dwayne Sanders for their reports!
Corn earworm moth catches in area black light traps averaged 2 to 45 per night. Please see the attached table for more details. blt_16_Aug_2018
Corn earworm moth captures in area black light traps are still increasing. Please see the attached table here: BLT_9_Aug_2018
Survival of corn earworm (bollworm) moths in the cypermethrin vial tests increased slightly this week, making the seasonal average = 21.4%, with 360 moths tested to date.
Tarnished plant bugs have continued to be a problem in flowering cotton in some Virginia cotton fields. This week, scouts found 10 out of 30 fields above the bloom threshold of 2-3 plant bugs per drop cloth sample across Virginia’s cotton-growing region. Six of these fields averaged above the bloom threshold for the past two weeks (see map below). Dirty blooms may indicate plant bugs are present but should not be used as a threshold for spray decisions. Cracking bolls and observing internal boll injury in small dime and quarter-sized bolls is also a great indicator bugs may be present and causing significant damage. Internal boll injury includes raised warts or outgrowth on the carpel wall, small black punctures that usually match an external lesion, and stained lint. We recommend observing at least 25 bolls per field for internal injury in addition to drop cloth sampling to make informed spray decisions. Plant bug populations have peaked in mid-August over the past few years in Virginia so we recommend continued scouting during the coming weeks. Check out this video if you would like to see a short tutorial on drop cloth sampling.
Plant bug density averaged over two weeks from 24 July to 02 August 2018.
Plant bug internal boll injury symptoms.
Plant bug nymph feeding on a dirty bloom.
Corn earworm moth captures in black light traps continued to climb this week–please see the attached table (pdf document) for more details: BLT_2_Aug_2018
We have tested 246 corn earworm moths in our vial tests this season, with an average of 15% surviving a 24-hour exposure to the pyrethroid insecticide cypermethrin at 5 micrograms per vial. The line graph is available here: vial_tests_2_Aug_2018
At our research farm in Suffolk this week, we have been finding bollworm eggs in cotton terminals with some small larvae on squares and bolls. Please be sure to scout your fields!
Statewide, approximately 18% of ears were infested with corn earworm larvae. Corn is considered a nursery crop for corn earworm, allowing the pest to complete a lifecycle and then move on to other crops such as soybean, cotton, and peanut in August. There is a linear correlation between the infestation level in corn and the amount of soybean acreage that gets treated with insecticide for this pest. Please see the attached pdf for more details: CEW_survey_results_2018