Friday, August 23, 2019

Managing cotton aphids

Cotton aphids have been more common than normal this season in the Southern High Plains region. Aphids are present in more or less numbers in almost every cotton field. They are often found on the underside of leaves or feeding on the plant terminals. In several fields, aphid infestation is evident with the accumulation of honeydew causing the appearance of sticky and shiny leaf surfaces. I know of a few spots where aphid treatments were necessary. For the most part, however, aphid numbers remain well below economically damaging levels. Beneficial insects (e.g. lady beetles, green lacewing, etc.) are ubiquitous and are working their magic to keep aphid population growth in check. Fields that are treated with broad-spectrum insecticides earlier in the season may not have enough beneficials and will have to be monitored closely for potential aphid outbreaks.  

I would not suggest aphid treatment unless aphids are very numerous, and honeydew is accumulating. Give the beneficials and natural control (rain, aphid fungus, etc.) a chance before the treatment decision is made. Having said that, given the current hot and dry conditions, I wouldn’t let too many aphids suck the juice out of plants that are already under stress either. The action threshold is 40-70 aphids per leaf prior to first cracked boll. Late in the growing season and once open bolls are in the field, honeydew can accumulate on the lint of the open bolls. Even under low infestation levels, cotton aphids can excrete enough honeydew to contaminate the lint, causing “sticky cotton”. The threshold drops down to 10 aphids per leaf after the first cracked boll.

Suggested insecticides are listed in the “2019 Insect and Mite Pests Control Suggestions for Cotton" https://lubbock.tamu.edu/files/2019/08/2019-Cotton-Insect-Control-Suggestions_ENTO090.pdf

For detailed information, checkout our Cotton Aphid fact sheet: https://agrilifecdn.tamu.edu/lubbock/files/2017/07/Cotton-aphid_ENTO074.pdf
Cotton aphids

Cotton aphid colony on the plant terminal

Lady beetle larva

Leaf curling resulted from aphid feeding

Thursday, July 11, 2019

Texas High Plains Cotton: Keep Watch on the Fleahoppers

This is just a heads up that there have been a few reports of cotton fleahoppers in cotton. Cotton fleahopper adults are pale green to gray-green; nymphs are lighter-colored with reddish eyes. Fleahoppers prefer to feed on small squares (pinhead size) and can cause substantial square loss if present in enough numbers. When scouting for fleahoppers, pay attention to both number of insects in field and the percent square retention especially during the first three weeks of squaring. They typically don’t target large (> matchhead size) squares.  Thus, they are normally concentrated in the top few nodes of the plant. Scout by visually inspecting plant terminals, the top three nodes. Adults are active flyers, but nymphs can be spotted when observed carefully.  
Cotton fleahopper adult (Photo: Salvador Vitanza)
Cotton fleahopper nymph (Photo: Xandra Morris)

Here is a link to a video on how to scout for fleahoppers in cotton.
Use an economic threshold of 25-30 cotton fleahoppers per 100 terminals to determine when treatment is needed. After, first bloom, fleahopper control is rarely justified. Avoid using broad-spectrum insecticides as they can negatively impact beneficial insect populations and cause outbreaks of aphids and bollworms.
Additional information on cotton fleahopper management can be found at: https://agrilifecdn.tamu.edu/lubbock/files/2017/06/Cotton-fleahopper_ENTO073.pdf
FYI – I am also seeing some black fleahoppers in cotton. There isn’t much information available about their impact on cotton—include them along with cotton fleahopper counts and base your treatment decisions taking into account the number of insects present and percent square loss.

Lygus bug (pictures below) numbers have remained sparse so far. But there have been scattered reports of treatment level infestations of lygus bug in few fields. Be alert for lygus but do not confuse other harmless true bugs for it.  

Adult lygus bug (Photo: Pat Porter)
Adult lygus bug

Wednesday, July 10, 2019

Sugarcane aphid has arrived, fall armyworm flight very large

Small colonies of sugarcane aphids have been found on grain sorghum in Lubbock and Hale counties in the last two days. Greg Cronholm, Independent Crop Consultant in Hale County, texted last night and reported finding a few small colonies. I found some today on blooming sorghum on the Experiment Station in Lubbock. Scouting and management guidelines are here.

Fall armyworm trap captures continue to be very high; more than twice the eight-year average.

 To put the current flight in perspective, the graph below shows what we faced at this time in July over the past few years. The magnitude of the current flight strongly suggests that fields be scouted for larvae and damage.

Wednesday, July 3, 2019

Big Fall Armyworm Flight Underway

The weekly fall armyworm pheromone trap graph shows a capture 2.35 times the eight year average.

Of interest, an average of 100 of these 310 moths were caught last night, so we might be on the front end of the second big flight this year. This would be expected, as many of the moths are probably progeny of the big flight the last week of May.

Yellowstriped armyworm captures in the western bean cutworm traps continue to be high, and I got a call last week about YSAW quickly defoliating greenhouse tomatoes.

Greg Cronholm, Independent Crop Consultant in Hale County, texted this week to say he was finding the first western corn rootworm adults of the season.

Friday, June 7, 2019

Moths and bugs: A strange start to the season

The 2019 season is beginning on an odd note. First we had an unusually heavy flight of fall armyworms, and the larvae are easy to find in early corn and sorghum. Then this week my western bean cutworm traps began picking up large numbers of yellowstriped armyworm (YSAW) moths (70 in one night). It has been several years since I ran pheromone traps for western bean cutworm, and in the past they did not catch yellowstriped armyworm. Either the pheromone lure has changed over time, or the lures have always been partially attractive to YSAW and we just have a lot of them in the system this year.

Male yellowstriped armyworms from the pheromone trap.

Next up we have unusually heavy populations of stink bugs. There have been several calls about Conchuela stink bugs in wheat and rye, and Dr. Ed Bynum addressed this in his newsletter earlier this week. Monti Vandiver, Syngenta, sent us a photo of some species of green stink bug at his home. We have yet to detect large numbers of these in the field.

In summary, 2019 is starting off as a buggy, wormy year.

Last summer I described large numbers of western corn rootworm beetles and damage associated with their larvae in corn planted near Hart, Texas all the way up to the northern Panhandle. At that time I said we would know their resistance status to mCry3a Bt corn in June of 2019 because we had made a collection and sent it to a USDA lab for resistance bioassay. As it turns out, the field where these insects were collected did not quite reach the formal threshold to be declared "Unexpected Injury", so the seed companies involved (the company that sold the seed and the company that owns the rights to the toxin) would not authorize the resistance bioassay to be conducted. They are not obligated to do so when a field is not an official UXI, although of course it would be most useful to know whether we have resistance to mCry3a or not. 

Non-rotated corn fields in the areas affected last year should be ok if planted to hybrids that contain Cry34/35. Fields planted to mCry3a (only) corn, or perhaps Cry3Bb1 (only) corn, should be closely monitored for root pruning and lodging. We expect beetle emergence from corn to begin in a couple of weeks.

Tuesday, May 21, 2019

Texas High Plains cotton: Time to scout for thrips and wireworms

With the cotton planting in full swing and the early-planted crop making its way up, it is time to begin scouting for early-season insect pests. Wireworms are a growing problem in the region especially in fields with reduced tillage and those following grain crops. Wireworm larvae damage cotton by feeding on the root, hypocotyl (stem of the germinating seedling), and cotyledon of plants before emerging from the soil. Wireworm injury usually results in stunting; however, heavy pressure can kill plants and reduce plant stand substantially. There are no rescue treatments for wireworms--early field scouting will help making timely replant decisions if necessary.

Wireworm injury (Photo: Pat Porter)

Thrips are the number one insect-pest of seedling cotton in the region. Their feeding causes foliar deformity (leaves crinkle and cup upward), plant stunting and delays in maturity. Thrips species composition in the Texas High Plains region is mainly formed by onion thrips and the western flower thrips. Preventive insecticide seed treatments provide good control against these species up to 3 weeks after planting. However, this can vary with growing conditions and the weather. When scouting for thrips, there is truly no substitute for whole plant inspections from a representative sample from across the whole field. It is important to remember that there will always be adult thrips on cotton. If plants are growing well, presence of adult thrips alone will not warrant foliar insecticide application. The presence of immature thrips (wingless) is a good indicator of whether the seed treatments are running their course and reproduction is taking place. Consider applying a foliar insecticide at the first or second true leaf stage when the emerging leaf shows signs of thrips injury and especially if immature thrips are present. Also, beware of “look-a-like” thrips symptoms from sandblasting, residual herbicides and high temperatures. As the cotton emerges, it is very important to keep a close watch at the early season pests to make timely management decisions and give a good head start to the crop.

Thrips injury

Additional information on thrips management can be found at: http://lubbock.tamu.edu/files/2017/05/ENTO-069_fn.pdf

Check out a video to learn how to scout for thrips:

Monday, November 19, 2018

Bt Corn Seed Selection in Light of Resistance in Corn Rootworm

By Patrick Porter and Ed Bynum, Extension Entomologists in Lubbock and Amarillo, respectively. 

The August 25th edition of this newsletter discussed how our mCry3a Bt corn was no longer able to control western corn rootworm in an area from Hart, Texas, north to the top of the Panhandle. In that newsletter, even though we were seeing all of the classic signs of resistance, we used the term “probable resistance”, only because our laboratory assays on field collected beetles will not be completed until next year. 

In addition to mCry3a, that newsletter suggested that since there is cross resistance between all of the Cry3-type toxins (mCry3a, eCry3.1Ab and Cry3Bb1), none of these toxins could be expected to provide good control of western corn rootworm. Dr. Aaron Gassmann at Iowa State University, a leading authority on corn rootworm resistance, said, “Cry3Bb1, mCry3A, and eCry3.1Ab all appear fairly similar to the rootworm. Resistance to one is likely to confer resistance to the other two.” 

As seed purchase decisions are made for next year’s growing season, it is time to put the cards on the table and discuss options for corn rootworm management.

By far the best option is rotation to a non-corn crop. 

Rotation will result in death of the entire rootworm population in the field because the larvae will not have a suitable host on which to feed and they will die. Since our rootworm beetles don’t lay many eggs in non-corn crops, the field can be planted the following year with no risk of a damaging rootworm population. 

When rotating to a non-corn crop, the volunteer corn that germinates must be killed when small to prevent rootworms from surviving and developing to beetles. The surviving beetles might lay eggs and re-infest the field, and the presence of corn in the field could attract other beetles from a considerable distance.

Of course crop rotation is often not an option, so here are the answers to some commonly asked questions. These answers are based on a field being in the resistance zone for Cry3-type toxins. If fields were planted to these toxins for the last several years and had lodging and high numbers of beetles, then resistance is likely. 

Is there any difference between a Cry34/35 (only) hybrid and one that has both Cry34/35 and a Cry3-type toxin?

It is better to plant corn with a pyramid of toxins rather than Cry34/35 alone. Resistance to the Cry3-type toxins is not complete so, in pyramids of the two types, the Cry3 will still provide some measure of additional root protection over Cry34/35 alone. This “partial protection” will also help preserve rootworm susceptibility to Cry34/35 because some of the insects with resistance alleles for Cry34/35 will be killed by Cry3-type toxins and won’t pass genes on to the next generation. See the table below for a full list of Bt corn hybrids active against corn rootworm, and the type of toxin(s) they contain. 

Several studies by academics and the seed industry have shown that, in areas where there is resistance to Cry3-type toxins, pyramids of Cry3s and Cry34/35 do not benefit from the addition of soil applied insecticides. Similarly, in our area there is probably no economic benefit from using soil applied insecticides on pyramids of Cry34/35 plus a Cry3-type toxin.

If I can use a Bt corn that has Cry34/35 without a Cry3-type toxin, will my roots be protected? 

Probably. There is no known resistance to Cry34/35 in our area and root protection should be very good. However, there are some caveats. One caveat is that, due to resistance to Cry3-type toxins, some fields have enormous numbers of eggs in them and the Cry34/35 will be challenged. We have seen instances of significant root damage in Cry34/35 corn under heavy rootworm pressure. If a continuous corn field had extremely high numbers of beetles last year and adult control was not used, then it might pay to use a soil applied insecticide when planting Cry34/35 seed. 

The other caveat is that toxin expression is lower in plants grown under stress, so proper agronomic conditions need to be met if the Cry34/35 is going to do the best job possible.

What if I have resistance but have to plant a Cry3-type (only) toxin?

In this case expect damage equal to or worse than last year, as a higher percentage of the population is now resistant. (Winter rootworm mortality is usually not a factor in our area, and adult sprays last year provided only suppression of egg laying.) The use of a high rate of insecticidal seed treatment and an at-plant soil applied insecticide is strongly recommended. 

How much protection is provided by insecticidal seed treatments, soil applied insecticides, and beetle sprays?

The answer varies by the amount of insecticide on the seed, but even at the highest amounts available on commercial corn seed, protection will be insufficient at moderate and higher infestations. If soil applied insecticides have been used continuously when planting Bt rootworm corn hybrids and spraying for beetles, the rootworms could also have developed resistance to the insecticides. 

Until this past year Bifenthrin insecticide has been used almost exclusively for both soil applications and beetle sprays. This has put a lot of pressure for selecting rootworm resistance. Researchers from Kansas State University and the University of Nebraska has shown different levels of resistance to Bifenthrin in rootworm populations across Kansas and Nebraska. Steward EC insecticide, which is not a pyrethroid, has recently received a supplemental label as a foliar application for beetle control. 

Does corn without a rootworm Bt toxin have a place?

Corn without a Bt toxin is a good choice for ground coming out of rotation to a non-corn crop because the rootworm pressure will be essentially zero. The seed will be treated with an insecticide and fungicide similar to the Bt hybrids. Planting non-Bt corn in a field that had high rootworm populations the previous year is not a good idea, even with high rates of insecticide in the seed treatment and with soil applied insecticides used at planting. 

Unfortunately, seed companies have not put as much breeding effort toward their non-Bt hybrids, so in some cases the agronomics and yield potential are inferior to the Bt hybrids. This is not true across the board, so consult your seed dealer(s) to examine the yield potential of hybrids that do not have rootworm protection. 

The Bt toxins in every type of hybrid from every seed company are listed in the Handy Bt Trait Table