Just a short update on the thrips situation in Virginia cotton and peanuts – I have gotten several calls from growers and field scouts/consultants with questions about what the thrips are doing, and how the Temik and seed treatments are holding up given this strange season. It was very dry in April and early May to the extent that growers had to stop planting. This week that situation totally reversed itself with some areas (our research Center included) getting over 5 inches of rain. The rain has brought a lot of cotton out of the ground that had been sitting for several days in the dry soil, almost two weeks in some cases. In my plots, as in many growers’ fields, some plants had already emerged and are in the 1– to 2 –leaf stage, while others are just emerging. But the good news is that as of today, the Temik and seed treatments are holding well. I base this on the soapy-sample data (5 cotton seedlings per plot, 10 peanut leaflets per plot) from several tests we sampled this week.

In cotton tests (planted on May 4), Temik treated plots are averaging about 1.5 adults/5 plants and Aeris seed treatment plots are averaging about 2.5 – 3 adults/5 plants. This is compared to about 20-30 adults/5 plants in the untreated controls. So far, there are almost no larvae in any plots, but with these high adult numbers, we expect to see a lot over the next 2 weeks.

In peanut tests (planted on Apr 29), Temik treated plots are averaging about 1 – 2 adults/10 leaflets, compared with 15 – 25 adults/10 leaflets in the untreated controls. Larval numbers are also still very low, less than 1/leaflet even in the untreated controls. Again, these high adult numbers will result in large larval populations over the next couple of weeks.

But, for now, the in-furrow and seed treatments are holding. We are sampling some Avicta seed treated cotton plots later in the week so will have some of that data to share next week.

Until the rain last night (May 13), it was shaping up to be a worst-case-scenario for early season thrips pressure in Virginia cotton. With the prevailing dry conditions, and vacillating between unseasonably hot and cold temperatures, seedlings were either slow to emerge, or if emerged, were standing still. Slow growing plants have reduced root growth and are slow to pick up the systemic insecticides. Couple that with what appears to be, at least so far, a very active thrips population, and it was setting up to be a ‘perfect storm’ for thrips problems.
Last week we began to see adult thrips crawling on cotton seedlings and volunteer peanut plants (peanut seedlings emerging from last year’s crop in cotton, soybean and corn fields). We also set out a series of 3×5 inch sticky cards for monitoring adult thrips. We trapped over cotton and peanut fields, brought the cards in after 3 days, and counted over 100 adult thrips per card (counting both sides). A lot of them were not pest species, but there were plenty of tobacco thrips, our primary cotton and peanut pest. This week we sampled two peanut trials and one cotton trial for thrips (10 peanut leaflets per plot, and 5 cotton seedlings per plot)using our standard soapy-water sampling technique and found an average of about 1 adult and 0.1 larvae per plant in cotton, and 0.5 adults and zero larvae per peanut leaflet. These are very low numbers compared with where it will go from here, but shows that we are definitely at the beginning of what I call ‘Thrips Season’. We are already seeing evidence of thrips feeding damage on untreated cotton and peanut seedlings.
Last night’s rain, about 1 ¼ inches, fell across most of the cotton/peanut counties. Before that rain we were facing the problem of having fields with two crop ages. Cotton planted in rows where moisture was available is up and into the first, even second leaf stage. In areas of the same field where no moisture was available to seeds, plants are not up yet. A long gap between emergence dates results in plants being in different growth stages in the same field which greatly complicates thrips management decisions, that is, when to treat for thrips and where. The rain last night should go a long way towards clearing this up.

All is still pretty quiet in terms of cotton insects. Although plant bugs are out there, we know of only one field that was treated. Square retention is good in all the fields we have checked and similar reports are coming in from local crop scouts. Although you can find spider mites in most fields, none are even close to threshold. Aphids are also present, but in very low numbers. Rain (or lack thereof) may be the bigger issue in many areas. Cotton will be blooming soon, and we will begin to shift to sampling developing bolls for stink bug damage. More on that next week.

Having passed through ‘thrips season’, we are having a little relief from insect pests. So far, there have been almost no reports of mid-season pests like aphids or mites. One field developed aphids in pretty high numbers but by the time it was discovered, tiny parasitic wasps had killed many of them. If we see more than 25% aphid mummies (the dried remains of parasitized aphids), and no insecticide is applied that would kill the wasps, the wasps will usually completely eliminate the aphid population within a week to 10 days.

Will plant bug populations be higher this year due to the somewhat wetter conditions? This is being talked about south of us where they are having a wetter than normal season. It is thought that wetter years result in more weeds and alternate hosts plants where plant bug populations can increase. However, most of our cotton area did not receive excessive amounts of rainfall, and some areas are actually getting pretty dry. We are seeing tarnished plant bugs in weeds and crop fields, but not in unusually high numbers. We are just beginning to assess fields for square retention, which is still the best way to determine the need for any action against plant bugs. Plant bugs feed on developing squares causing them to blacken and drop off, leaving a telltale scar where the square had been. With some training, it is fairly easy to inspect a cotton plant and find either blackened squares or the scars where squares were. We consider a field in the ‘safe zone’ if square retention is 80% or above. This is because cotton can compensate from loss of as much as 20% of the total square load without any reduction in yield. We proved this for ourselves some years back by doing a 2-year study where we removed up to 20% of the first position squares, on several varieties. No yield loss occurred.

As of this week, based on checking several fields and reports from field scouts in the private sector, our cotton fields are at greater than 90% square retention, which is what we generally see. A few fields to the south of us in North Carolina have been reported to be in the low 80% range, and one is at 75%. Plant bugs are spotty for sure, but all indications are that this year, like most, will be a low plant bug year.

The attached Word document contains data tables summarizing Dr. Herbert’s 2009 thrips research in cotton. Trials are still in progress. Additional information: cottonthrips-doc

Forget everything I predicted last week. Most of it was wrong. I had a mentor early on in my career who very wisely said, “If you try to predict insects, they’ll make a liar out of you every time.” So true he was. Last week I suggested that we might have a relatively light thrips year; that based on the excellent soil moisture and warm growing conditions up to that point, cotton might grow so quickly as to not need extra foliar sprays. Two major things have changed. One, the weather took a dramatic turn to the cool side. Since May 11, we have had five nights in the 40s&not good cotton weather. We have continued to get rain, heavy in some spots, with up to 3 to 6 inches in single events. Most of our cotton is germinated, in the 1st to 2nd true leaf stage, but the cold weather has it ‘sitting still’. To make matters worse, thrips populations are increasing. As I said in last week’s email, we are using yellow sticky cards to monitor thrips populations in five locations across our cotton region. We check and replace the cards two times each week, on Mondays and Thursdays. The counts are up (see the attached line graph with sticky card data counts from the 5 locations), and based on what we know from sampling over the past few years, the peak has not occurred. When cotton is growing so slowly, plants are very vulnerable to thrips feeding. Thrips concentrate their feeding on the tiny seedling bud, or growing point. Just a few days of intensive feeding can have dramatic effects by stunting plants, greatly slowing maturity, or in really bad cases, will even kill the seedling. And in our experience, when plants are ‘sitting still’ it does not take many thrips per plant to cause significant damage.
So what should growers do? Scout fields and consider a foliar treatment if more than 10% of plants have noticeable damage to the bud. Damaged buds will be deformed and blackened. Bud damage indicates that whatever was applied at planting, seed or in-furrow treatment, is no longer doing the job. Fields that had heavy or continued rains will be at the highest risk as any planting time insecticides will most likely be washed out of the system. I have been asked about what to spray and how much. To date, our best foliar control has been obtained with acephate (e.g., Orthene). Pyrethroids do a good job, but never quite as good as acephate. Each year we do a lot of cotton thrips trials and we have yet to see an Orthene failure. But, it has happened on a few growers’ fields where western flower thrips have become the primary pest species. Orthene does an excellent job of controlling tobacco thrips, still our primary pest species, but does a poor job on western flower thrips. Pyrethroids are no better, even worse in some cases. To date, we have only seen ‘westerns’ as the primary pest species in a very few fields. The great majority are still infested with tobacco thrips, which means they can be protected with 4 to 6 oz of Orthene per acre. We recommend that broadcast sprays go out with enough volume to achieve good coverage of the seedlings. I tell folks that good coverage means seedlings should be completely wet after the sprayer passes over. Higher rates of Orthene are not needed for tobacco thrips, and higher rates are not more effective on ‘westerns’. Last year we found that the best product for controlling ‘westerns’ was Radiant SC (a Dow AgroSciences product). This would be a costly choice and only warranted if a good thrips sample and identification by a lab verified the problem. Let’s hope ‘westerns’ are not a big issue this year. Based on what we know today, we are still recommending the ‘old standards’. Additional information: stickycards-mar21-09-ppt