Wednesday, June 20, 2018

Sustained High Numbers of Fall Armyworm Moths

This week's fall armyworm pheromone trap graph appears below. The 7-year average for this week of June is 110 moths per week. This week's capture was 707.

This does not appear to be a phenomenon confined to the Lubbock Research Center, as Katelyn Kesheimer, EA-IPM in Lubbock and Crosby counties, reported several hundred moths in the Crosby County traps she operates. (Rain filled the traps so it was not possible to count all the moths, but there  were hundreds.) Additionally, Blayne Reed, EA-IPM in Hale, Swisher and Floyd counties, drove to Plainview from College Station late last week and reported that fall armyworm moths were very abundant at rest stops along the way.

A prior post from April of this year discussed some genetic work being done by Ashley Tessnow, a graduate student in the Dept. of Entomology at College Station. She determined that the Lubbock area fall armyworm moths we sent her last year were 30% rice strain and 70% corn strain as a season average. She also noted that the relatively big flight toward the end of June last year had 93% corn strain.

We don't know where these moths are coming from. Some are doubtless progeny of the moths that arrived here earlier in the season, but it is likely a majority of the moths caught this week have come up from south Texas. Ashley's work will ultimately help us to know the geographic origins of our moths.

Most Bt corn will not get appreciable damage, but non-Bt corn should be scouted. Yesterday I noted that there were a lot of newly hatched larvae in my non-Bt corn at the Experiment Station just as the oldest larvae were cycling out. Actually there were a lot of plants infested by larvae from egg masses that had hatched in the last 24 - 48 hours. Some of these newly infested plants had four or more larvae per whorl and may get "dead heart" due to the very high numbers of caterpillars feeding on the youngest leaves in the whorls. Sorghum should be scouted as well.

Information on scouting and thresholds can be found for corn here and sorghum here. Essentially, both of these crops can withstand 30% whorl damage before an insecticide is justified. This does not, however, apply when deadheart is likely to happen. There are a few fields of corn in the area that are silking now, and these should be scouted regardless of whether they are Bt or non-Bt. 

While scouting it would be a good idea to look for corn earworm eggs and larvae; the moths are very abundant in my whorl stage corn although I do not have any pheromone trap data to report. 

Friday, June 15, 2018

Fall Armyworm Trap Captures Very High at Lubbock

My post two days ago said fall armyworm captures in pheromone traps were a bit above average and that it seemed we were at the start of a big flight. The traps were emptied on Wednesday, and today they had an average of 215 moths per trap.

To put this in perspective, the 7-year average for this week of the season is 115 per WEEK. So in just two nights the capture we are already 87% above the historical weekly average. There is no way to know if the numbers will remain at their current level for five more nights, but if they did then next Wednesday I would report 752 moths per trap.

Regardless of how things go for the next five days, we are now well above the 7-year average. My non-Bt corn is taking significant damage, and this is before most of the caterpillars are anywhere near large. Egg masses are easy to find.

The good news is that fall armyworm is not generally a big problem very far north of Lubbock. My colleagues and I checked research plots with non-Bt corn at both Halfway and Bushland this week and found very little damage from either fall armyworm or corn earworm. However, this might not be the case next week, especially at Halfway.

Wednesday, June 13, 2018

Mid-June: Mostly Good for Corn and Sorghum, Fall Armyworm High

It is mid-June, and I am pleased to report that there have not been any serious insect problems in corn and sorghum yet. Well, let me temper this by saying that the drought has brought plenty of problems outside the entomological realm.

Wireworms have been a problem in spotty areas, but for the most part seed treatments have kept them in check. Corn in the area is approaching V6 - V8, and sorghum is anywhere from V5 to still in the bag. Sugarcane aphids have not been detected on the High Plains, but sorghum planted relatively late will benefit from seed treatments to control sugarcane aphids, at least if prior years are a predictor. The progress of sugarcane aphid can be tracked here.

Fall armyworm trap captures just jumped up, and the weekly average exceeds the 7-year average at Lubbock. We may be at the start of a big flight; last night's capture was 124 moths per trap, whereas the nightly average for the prior six nights was only 25.4.

I have non-Bt heirloom dent and sweet corn planted at the Lubbock Experiment Station, and the caterpillar damage is moderate or worse depending on the variety or hybrid. (These old varieties, the ones without any insect resistance, give me an idea of the "worst case" of what is happening.) I have been monitoring modern field corn in the Lubbock area, and non-Bt hybrids have had only light to moderate fall armyworm damage for the most part. The worst I have seen had an average rating of 5 on the Davis 0-9 scale, with zero being no damage. There were pockets of plants with 7-8 damage. The Bts have been holding up and show little damage.

The good news in corn is that we still don't have any indication that our Bts are breaking down on the High Plains. In more southerly parts of Texas and elsewhere in the south, Bt corn is showing considerable susceptibility because corn earworm (cotton bollworm) has become resistant to some of the Bt toxins. However, we have no evidence that those resistance genes have made it here to any great extent. Most of our area corn is Bt, and this means that fall armyworm and corn earworm (and southwestern corn borer) will not pose a threat in the whorl stage.

In summary, things are pretty good at the moment, except for fall armyworm. Small colonies of spider mites have been found, but they have disappeared, probably due to predation by thrips coming off of wheat. We will continue to watch for the arrival of sugarcane aphids in sorghum; they hit in the third or fourth week of June the last two years and required treatment starting in mid-July, but every year is different and this year feels like they might be late.

Friday, June 8, 2018

Should I be on the lookout for thrips?

I have noticed some thrips damage on the early planted cotton especially in the areas north of Lubbock. Fields that have already reached 4 true-leaf stage are pretty much safe from further thrips damage. We still, however, have a lot of late-planted cotton in South Plains that ranges from emergence to 1st or 2nd true-leaf stages which are very prone to thrips injury. Late planted cotton usually escapes peak thrips flight but the fields at the most vulnerable stages especially those in the vicinity of maturing wheat or pastures will have to be watched closely for thrips.

In general, with the current hot and mostly sunny days, I would not be too aggressive when it comes to spraying as cotton plants can outgrow thrips under good growing conditions. Having said that, I wouldn’t wait too long either if the damage is being done. Spraying for thrips after the 3rd true-leaf stage contributes little towards the yield—so the timing is critical!

What are thrips?
Thrips are early-season pests of seedling cotton. They are numerous in cotton grown near maturing small grains (wheat) or seedling corn. Thrips attack leaves, leaf buds, and very small squares (flower buds), causing a silvering of the lower leaf surface, deformed or blackened leaves, and terminal and square loss. Feeding most often occurs in the new terminal growth and on the underside of the leaves. Their feeding ruptures cells, causing stunted plants and crinkled leaves that curl upward. Severe infestations can destroy terminal buds, causing excessive branching of the plants and delayed plant growth.
No damage to severe thrips damage

How do I scout for thrips?
Begin inspections once the cotton reaches approximately 50 percent stand emergence. Thrips can migrate in great numbers from adjacent weeds or crops, especially small grains (wheat), and cause significant damage within a few days. Randomly select 20-25 plants from different parts of the field and closely examine them, looking for adult and immature thrips. Look carefully through the terminal growth, picking it apart with a pencil lead or other pointed object, uncurling all the leaves—thrips often hide in tight locations, especially during rainy, windy conditions.
Thrips on plant terminal
What are the thresholds and control options for thrips?
The threshold for thrips is 1 thrips per true leaf (i.e. at 2 true leaves, it would be 2 thrips per plant; at 3 true leaves, the threshold would be 3 thrips per plant and so on). Research shows that applying foliar sprays after significant thrips damage has occurred results in little or no benefit. Base your decision to apply insecticide on the number of thrips present and the plant development stage. Foliar insecticides for thrips provide maximum benefit when applied at or before the second true leaf emerges. Sprays at the four and five-leaf stage after the damage is already done are typically for revenge, rather than yield.

Seed treatments with neonicotinoids (e.g. imidacloprid and thiamethoxam) are still proving to be effective controlling thrips in the Texas High Plains region. However, under heavy thrips pressure, foliar treatment is often needed on the top of seed treatment. Presence of immatures and injury symptoms on plant are good indicators of whether the seed treatments are working or not. As far as foliar treatments are concerned, acephate, dicrotophos (e.g. Bidrin 8EC), and spinetoram (e.g. Radiant SC) all provide an excellent thrips control. You can tank mix your insecticide with a post emergence herbicide application. The decision you will likely make is whether to be timely for the weeds or the thrips. Remember, no insecticides are approved for tank mixing with applications of any dicamba products in cotton.