Texas LRGV: Watch for Whiteflies in Cotton; Sugarcane Aphid Numbers Building

Whitefly adults and eggs. Photo: James Castner, University of Florida

General Situation

This week we managed to scout in some farily dry fields but majority of LRGV is still very muddy due to the 8-12 inches received the previous week July 5-7th. Harvest continues in grain sorghum as the weather has caused for some interesting field conditions and I imagine most will be finishing up or barely be getting into fields that are still drying out by middle of next week.

Cotton

Seeing a lot of open boll cotton in lower half of the canopy as we scout fields across the Valley. Most fields we checked were at 10-12 NACB. Averaged total boll count per cotton plant was 10-13 total bolls per plant in most fields we checked in Cameron and Willacy counties.

We noticed leaf spotting occurring a few weeks back in the LRGV cotton and so I collected leaves this week and had our local plant pathologist Dr. Olufemi Alabi inspect them, and he noted two different minor leaf spot causing fungi – the Alternaria sp., and Stemphyllium sp. occurring on our cotton.

These fungi (Alternaria sp., and Stemphyllium sp) cause circular concentric lesions, can appear reddish in color, and have a shotgun hole like appearance on the leaves. These foliar diseases tend to be more prevalent at crop maturity and during periods of high humidity and some varieties are more susceptible to late season leaf spot fungi according to the Texas Plant Disease Handbook.

Having these two fungi present is also an indicator of a lack of potassium amongst other nutrient deficiencies. Late season occurrence of these minor leaf spot fungi has hardly any impact on yield and treatment is not necessary. However, the fungus can survive in the soil and debris so a good soil tillage program will be key from having it occur in the cotton crops in years to come.

This week in cotton was very clean as we were not really picking up on any pests. We did pick up on a handful of whiteflies in mid valley and along the river. Saw one cotton field in the San Benito area that was at threshold for whiteflies (adults and nymphs) and had notable sooty mold on the leaves.

Sooty mold comes from when black mold grows on the sugars being excreted by the whiteflies as they eat which can inhibit proper plant growth. Sooty mold can also degrade the lint value if rain wets it and causes to stain cotton.

I was also picking up on a handful of cotton aphids in the upper new leaf flush on tops of the cotton plants along the river in areas from Progresso to Pharr.

Majority of cotton fields have mature bolls present so the few stinkbugs and couple of plant bugs we saw are not of importance because they will not be able to penetrate mature bolls so easily.

Let’s be on the look out this next weeks for cotton aphid and whitefly populations to make sure they are kept low and in check and we make our way towards harvest.

Grain Sorghum

This week we came across several sorghum fields that were at threshold for sugarcane aphids. We found several fields glistening from all the sugars being excreted by the sugarcane aphids as they fed. We saw some sugarcane aphids migrating to the head. Several fields were reported to be treated soon either by plane or by ground as weather permits.

AgFax Weed Solutions


Remember when scouting for SCA that if the field average of SCA is 50-125 aphids or more per leaf, then it is recommended that you apply an insecticide within 4 days of finding this infestation level, much sooner if you are averaging 100 SCA per leaf or more.

Do note that sometimes applying glyphosate alone to dry the leaves down will only kill the SCA food source driving the SCA to migrate to the mature sorghum head and feed which can cause gumming and can clog combines.

I found high SCA populations everywhere from along the river in Progresso to middle of Mercedes, La Feria, Lyford, Sebastian, La Sara, San Benito, Los Fresnos and Raymondville. I also saw many predators controlling SCA as well. Scouting some of the younger sorghum prior to boot stage these fields were very clean free from SCA and worm pressure.

We did see some high rice stink bug pressure in soft dough sorghum in the Lyford and Raymondville areas.

This week seeing sprouting sorghum seed in the Rio Hondo, Los Fresnos, San Benito areas where we had the most rainfall present and in other areas of the Valley we are seeing minimal to no seed sprouting.




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