We are now hearing of threshold levels of corn earworm scattered across the region. Infestations are spotty. For example, we are not finding many worms in Chesapeake, VA Beach or Suffolk but have heard of infestations in several other areas. As many beans are still a long way from safe (R7), we may see more fields reach threshold as we get closer to Labor Day.
Author Archives: Ames Herbert
Soybean aphid outbreaks
Ed Seymore, our soybean aphid scout has reported finding above threshold numbers (500+/plant) of soybean aphid in fields in southwest Fauquier Co and northwest Culpeper Co. These aphid populations have been increasing over the past two weeks and are in late planted beans that are in the R3-R4 growth stage. This fits the scenario for a treshold, as best we understand it.
Corn earworm and pyrethroid susceptibility, soybean aphid, and Mexican bean beetle update
Corn earworm and pyrethroid susceptibility, soybean aphid, and Mexican bean beetle update
CORN EARWORM: Moths are continuing to exhibit high levels of survivorship in our adult pyrethroid vial tests (see the attached line graph). We are striving to test several hundred moths each week as we feel this is important information for growers. As of this week, we are hearing of some fields where growers are getting less than satisfactory results with their pyrethroid sprays.
Earworms are reported to be in peanut, cotton and soybean fields in our area. It is time for folks to begin scouting throughout the state. In areas that are mostly dry, the problem is worse. In wetter areas, numbers are slower to build. The moth flight is increasing gradually, but has still not peaked. Rains are keeping the corn green, which tends to hold them in the corn, and in general, moth activity is less during rainy periods. Moth activity is higher in dry areas. If things dry out over the next two weeks, we can expect a large flight. But if it stays wet, the moth flight and subsequent earworm numbers will be suppressed.
SOYBEAN APHID: Weather conditions (generally cool in the low to mid 80s/wet) are nearly perfect for soybean aphid survival in some parts of the state and consequently, we are getting reports of high numbers in some areas. We will provide more detail next week, but as of today, many fields in the Gloucester/Mathews area, the Goochland area and the Shenandoah Valley have populations. I recently spoke with one of the entomologists in the north central states who was part of the large effort to develop the soybean aphid thresholds and here are his main ‘talking points’. Thresholds only apply up to the R5 growth stage. After that, beans can withstand 1000s per plant with no detectable problem. From R1-up to R5, the threshold is 250/plant IF POPULATIONS ARE INCREASING. Even maintaining at 250/plant does not result in a yield loss. An insecticide application at 250, when populations are increasing, prevents that increase. This is an important concept to be aware of. It takes consecutive field visits and good record keeping to determine if the population is holding, increasing, or decreasing due to predation by predators (lady beetles for example). He also warned that tank mixing an aphid insecticide (a pyrethroid) with a herbicide will only provide aphid control if the spray system is set up for high volume (10 + gpa) and small droplet size. The large droplet systems used for herbicides will not work well for aphids. Hollow cone spray patterns with small droplet size are needed to get product to circulate throughout the soybean canopy, to the undersides of leaves where aphids are feeding.
MEXICAN BEAN BEETLE: Prior to when I came to Virginia (in Aug 1988) Mexican bean beetle had been a major pest of soybeans. For a number of debatable reasons, in the years just before I arrived populations crashed. Since then I have seen them a total of two times in isolated areas, only in years and areas where it stayed wet and cool (relatively) all summer. Galen Dively in Maryland reported today that they are seeing a few outbreaks on the Maryland Eastern Shore. As cool and wet as it is in some parts of Virginia, it would not surprise me to hear of a few outbreaks. Keep a watch out for them. They do the worst damage when they go undetected in the first couple of generations. They gradually build to higher and higher numbers until the last generation, and in what appears to be ‘overnight’ they can totally defoliate a soybean field¬ a pretty sight.
Additional information: cew-cyper-aug-13-09-herbert-ppt
Peanut insect pest update, potato leafhoppers on the move
It is worth noting that potato leafhoppers are active in some peanut fields. In some of our plots, especially those that were not treated with in-furrow insecticides for thrips, we are approaching threshold levels of damage. Our recommendation is to treat fields if 20-25% of leaves show typical hopper burn leaf damage symptoms (the yellow V-shaped pattern on the leaflet tips) and hoppers are still present in the field. It is important to determine if leafhoppers are still present because we have found that they typically migrate into and back out of peanut fields throughout the season, and may not actually be present even when leaf damage symptoms are obvious. Mid July is a fairly common time to begin seeing thresholds, if they are going to occur. We recommend checking fields just prior to making other sprays (example, leafspot) so insecticides can be tank mixed if a threshold for leafhoppers is detected. Several pyrethroid insecticides are listed for potato leafhopper control. Also, Lorsban 15G will provide some control, if applied for soil insect control.
Cotton insect pest update
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.
Our corn earworm pyrethroid susceptibility monitoring program indicates a possible problem in the making
As you may recall, each year we assess the susceptibility of corn earworm to pyrethroids using the standard AVT (adult vial test) process. This involves collecting live moths using pheromone baited traps from multiple locations across the area. Moths are individually placed into vials pre-treated with cypermethrin (the standard used across the southeastern states) and assessed for mortality after 24 hours. If moths survive this 24 hour exposure, they are considered to be ‘resistant’. The percentage of those that survive provides some indication of what growers might expect to see when they apply pyrethroids to crops (soybean, cotton, peanuts). Although not a perfect system for determining actual resistance levels in the population, this procedure does provide valuable insight. For example, last year we had unusually large numbers of survivors. Whereas in previous years we had seen 5 to 10% survivors, in 2008, survivorship in late June exceeded 20%, and then increased to over 40% by August. Over the course of the summer, we received several calls about spray failures: cases where application of normal rates of commonly used pyrethroids did not provide adequate levels of corn earworm control.
So, what is the situation this year? Things do not look good. We started the season in early June with less than 10% survivors (see the attached line graphs, 2008 on the left side, 2009 on the right side) but are now at over 30% survivorship, even higher than at this time last year. Granted these data are based on a very small subsample of moths (744 moths to date), but all indications are that we may be in for some problems. Of course things could change as we progress through the season. We will continue to provide updates.
Additional information: mean-weekly-cew-moth-survival-jul-2-09l-ppt
Cotton insect pest update: few plant bugs and good square retention in fields
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.
Thrips update for cotton, peanuts and soybean
As of this week, thrips numbers have decreased in cotton, and plants have grown out of the thrips-susceptible window. We have had good rainfall, temperatures are good and most cotton is at the fifth leaf stage or beyond. We have terminated our cotton thrips sampling and ratings for the season. The attached line graph provides the sticky card data and shows the decline in adult catch across the region.
Peanuts are still at risk. As predicted last week, immature thrips numbers have increased in peanut. We are expecting pressure to continue for a least another week to 10 days. In our plots, Temik and Thimet are holding well. For example, in one field trial where we are comparing Temik 15G at 7 lb/acre, Thimet 20G at 5 lb/acres, and some experimental compounds, in the June 9 sample, there were 81 immature thrips/10 leaflets in the untreated plots, 8/10 leaflets in the Thimet treatment, and 7 in the Temik treatment. Untreated peanuts are reaching about a 5.0 on our 0 to 10 plant injury scale (where 0 = no damage and 10 = dead plants). A rating of 5.0 means that almost all leaves are crinkled from thrips feeding and most of the terminals show darkening/blackening. We generally expect yield reductions if ratings get much higher than 5.0, and we will definitely see injury exceed that by next week (given the high number of immatures). But again in our plots, both Temik and Thimet are holding well. We are seeing a big difference among the foliar applied insecticides in terms of thrips control and plant injury. In a nut shell, Orthene 97 and Radiant SC are providing good control as evidenced by the lower plant injury ratings. Karate Z is not performing well in either our cotton or peanut trials.
The thrips situation is very different in soybean. We have several trials across the state assessing both seed and foliar treatments. In soybean, our standard sample consists of 10 leaf trifoliates per plot. As of this week, we are getting averages of about 8 to 15 adults and 30 to 50 immatures per sample. The species break down is also different from what we are used to seeing in cotton and peanut. In those crops we normally see 90% + tobacco thrips. In soybeans, we are finding a mix of about 40% tobacco thrips, 50% soybean thrips and 10% other (eastern, onion, other odd balls). We are taking a lot of data this week and next to track the results of our treatments. Thus far, the seed treatments have a lot fewer thrips compared with untreated plots. Although we are finding a lot of thrips on soybean, we see very little actual plant damage. To date, we have never been able to show a yield response from controlling thrips in soybean. With a coordinated effort, this year we will be able to add several more thrips/soybean yield assessments to our data. We will post these results.
Additional information: stickycards09-ppt
First results from our corn earworm AVT pyrethroid monitoting program
To date we have tested about 450 corn earworm moths collected from two locations (Sugffolk and Southampton Counties). So far, results are prmising with only about 5% overall survivorship. Anything below about 20% is considered low risk in terms of potential field control problems. So we are starting at a good point.
Thrips in cotton, peanut and soybean
Thrips populations are still increasing. But, in cotton, the treatments seem to be holding, and cotton is growing. The recent rains in many areas may allow cotton to grow through the problem. We are finding a lot of thrips in soybean, and we hear that many growers are treating for them. But even with the leaf ‘silvering’ and ‘crinkling’, we have never shown a yield advantage from treating soybeans for thrips. Treatments will certainly green them up, but is that worth the cost, with no added yield advantage? In peanuts, we are expecting damage to get quite a bit worse in the next week. We are still finding more adults than immatures in our peanut leaflet samples. These adults will beget a lot of immatures. Peanuts should be scouted next week at the latest.