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Southeast Missouri Pest Bulletin July 1, 2003

INSECTS & OTHER PESTS
I've received a few calls regarding infestations in corn (corn borers) and cotton (aphids, plant bugs, spider mites) fields. Moth counts (Table 1) in pheromone-baited traps remain low but steady this past week. (MLB)

CORN
Corn Borers: I have not received any more calls regarding European and Southwestern corn borer infestations in the past few days. Based on the trap counts I've received as of today we are probably between generations; therefore, it will be necessary to intensify scouting efforts within the next two weeks.

COTTON
Crop Report: It's clear looking at this year's crop that it is behind the normal growth pattern for southeast Missouri. This is backed up by our DD60's, we have only received 612 DD60's since May 1st of this year versus 804 in 2002. A comparison of DD60's for this year versus 2002 is reported in Table 2. (BP)

As bad as our crop may seem, it's better off than in other cotton production regions of the country. I just returned from Lubbock, and they have lost 1.1 million acres to hail damage. All I saw was June cotton that will have low yield and micronaire, and it will likely receive a large discount due to the low micronaire. The rest of the fields have been replanted to sorghum including my dad's farm. With the lack of water and fuel costs so high since it is 300 feet down to water table, the crop will not be adequately irrigated and will most likely yield 2500 pounds. Farm incomes will be low this year. So, our crop is better than I initially thought. It is kind of like the story of the man with no shoes, he was sad until he saw the man with no feet.

We also have observed yellow cotton in many fields, especially on sandy areas. Soil and tissue tests indicate that it is probably due to a sulfur deficiency. A soil application of ammonium nitrate should help without risk of leaf injury. A foliar application of products such as potassium thiosulfate could help but you run the risk of leaf burn unless it's applied with a center-pivot sprinkler system.

Aphids: I've received a couple of reports of aphid treatments going out this past week. I certainly hope the aphid's natural enemies will help keep aphid infestations under control, but I want to remind you a combination of different parasitoids and predators are usually required to keep aphid infestations at subthreshold levels. (MLB)

Any labeled, recommended insecticide should be applied at maximum volume (5 gallons by air and as many gallons as possible with ground rigs) with hollowcone nozzles so to thoroughly coat the plants. Again, if you select decide to use one of the neonicotinoid insecticides (Centric, Intruder, or Trimax), avoid the temptation to use lower use rates. This will only decrease the products' effectiveness, and it mostly mean a higher insecticide bill for you in the end. You are better off banding full use rates NOT decreasing broadcast rates.

Plant Bugs: Tarnished plant bugs continue to be abundant in weed hosts [particularly plains coreopsis (red and yellow flowers)] that border cotton fields. As I mentioned last week I strongly recommend that you don't destroy these weed hosts if your crop is producing squares. You also should watch for plant bugs switching from weed hosts to squaring cotton when these weeds are killed with herbicides within a field. I've seen several cotton fields with healthy stands of plains coreopsis, and as I mentioned before this is an excellent host for plant bugs. Missouri action thresholds for rescue treatments are: 6-8 plant bugs per 100 row feet during the 1st week of squaring, 8-10 per 100 row feet the 2nd week, 12-15 per 100 row feet the 3rd week, and 15 or more per 100 feet during the 4th week.

I realize with this year's delayed crop, there will be a temptation to retain all the square's your crop can produce. I certainly understand this sentiment, but realistically a square retention rate of 80-90% is more economically viable. I hope you keep this in mind when spraying for plant bugs and other insects.

Herbicide Layby: Before I make any comments on post-directed, layby chemistries for cotton, we need to stress the importance of traditional layby treatments. In Roundup Ready soybeans, you can do wonders with a couple of shots of glyphosate. But cotton is planted thinner, grows slower and shades less. Since glyphosate has no residual weed control - new weeds will emerge and grow late in the season; therefore, post-directed and layby treatments still are as important as ever. At least one of the herbicides you are spraying needs to have some residual activity. (AK)

There is a lot of terminology and jargon surrounding post-directed and layby applications in cotton. These terms are even loosely married to certain equipment and spray-nozzle setups. Post-directed can mean two nozzles, layby can mean a single nozzle, and then there are hooded applications. Regardless of the equipment, the concept is the same - you are carefully spraying something underneath the cotton foliage because these herbicides will injure cotton if sprayed directly on the foliage. The equipment just differs on how much protection it provides the crop from the spray. Nevertheless, the set up and adjustment of whatever equipment you use is very critical, as is a healthy height differential

Twenty years ago, establishing and maintaining a height differential was critical and tricky. Today, it is just as critical. It's a little bit easier with Roundup Ready cotton, but it still isn't Bubba-proof. You can quickly loose your cotton-weed height differential if the weather delays your application.

Even though Bladex isn't available anymore, there are six other fairly good, post-directed herbicides we can use. The bad news is that none of them are quite as good as Bladex. We're going to discuss the differences between these, but you should remember that a lot of this is hair-splitting. All of these products do a good job in post-directed/layby tests we conduct every year; however, when you take several years worth of information, some subtle differences emerge.

Currently, the Karmex-based herbicides are most popular. Karmex is not available by that name, but Direx and many Diruon-based compounds are. The price is hard to beat. In our test plots Diuron-based products do a good job, but some growers have commented that they needed better broadleaf activity. That leads to our key question: How good is good enough, and only you can answer that question. If your late-season weed control program is fine, stick with it!

Another popular post-direct/layby herbicide is Caparol (also sold as Cotton Pro and other prometryn herbicides). An advantage to Caparol is that it has slightly better Palmer amaranth activity than Karmex-based products.

Goal is usually one of our better layby treatments. It has good activity on morningglory, cocklebur and pigweed, but can be weak on prickly sida/teaweed. It's quite hot on cotton and you need to be extra careful when adjusting your sprayer.

Valor is still in experimental stages and recent requests for Section 18 labeling were denied by the EPA. Valor has been among our better post-directed herbicides, but on the other hand, it hasn't out performed any of them either. Reflex is still mentioned on occasion by Syngenta for a possible label. It has performed well in tests, but, just like the Valor, we already have herbicides that do much the same thing.

Cobra, Aim and Harvade are often mentioned as layby additives. These herbicides can add postemergence activity on certain weeds, but the key to layby is residual activity. Use these if you need them, but they aren't the meat of a post-directed treatment.

Over the last few years, we've been testing Cotoran (fluometuron) in the late-post-direct/early layby window. Cotoran once was used more as a preemergence and early post-directed treatment, as opposed to the later applications. It has performed very well. Cotoran, Karmex and Caparol are all somewhat related to each other, and Cotoran has always been the best. But, its price does reflect that. It has performed well in post-directed layby window too. It has the best morningglory activity of the three "photosynthetic inhibitors".

An area worth debating is the addition of DSMA/MSMA versus the addition of glyphosate in the post directed spray. Oddly enough, these herbicides are very different, but in this scenario, they are both there for grass control. If you've got a few grasses, the two herbicides are pretty much the same. If you have problems with nutsedge or volunteer Roundup Ready soybeans, MSMA has a slight edge. If you have big problems with grass, glyphosate has the edge. Since herbicide rotation is a very popular subject, this is a good opportunity to give glyphosate a rest and use DSMA or MSMA.

The bottom line on post-directed layby treatments is that it is important to use something with residual activity and apply it on time.

GRAIN SORGHUM
Corn Earworm: With sorghum fields starting to bloom and produce seed heads, these fields will be susceptible to corn earworm infestations. Seedheads are most susceptible to insect damage during the bloom to milk stages. Researchers have determined that an average of one larva per seedhead can reduce yields by 5% and two larvae per seedhead can cause a 9-10% yield loss. Once sorghum begins to bloom, fields should be monitored every 5 days until the hard dough stage. Randomly sample 10 plants at each of 10 locations per field by vigorously shaking the seedheads over a beat-sheet or preferably a 5-gallon plastic bucket. This method will help you detect the smaller larvae (less than 1/4-inch in length) that are easily overlooked with visual examinations. The action threshold for sorghum is when more than 75% of the plants are infested with one or more corn earworm larvae per seedhead. (MLB)

Sorghum midge: This is another important grain sorghum pest once plants start to bloom. Late-planted or sequentially-planted fields will be more at risk than early-planted ones. Midge larvae damage developing seeds and this reduces seed quality and yields. The best time to scout sorghum fields for the midge is during the morning when winds are calm and the adults are most active on the flowering heads. Sample 10 heads at each of 10 locations per field to determine the extent of midge infestations. The University of Missouri action threshold is one adult midge per seedhead.