Web Site: http://entowww.tamu.edu
Vol. 30, No. 8

COTTON

Cotton continues to make progress even with the lack of rain and 90 F + days. Some of our abundantly watered cotton still has 5 to 7 nodes above white flower. Many fields have dropped to 4 to 5 nodes above white flower and are approaching cutout. Cotton with limited water resources has bloomed "out the top" with 1 to 3 nodes above white flower. Fields which have been short of water now have extensive fruit shed, with some losses exceeding 60%. This loss includes all sizes of squares, blooms and small bolls up to the size of a nickel. Some of the shed can be attributed to plant bugs and bollworm damage, but overall this accounts for only a small portion of the loss. As cotton enters into drought stress it adjust the fruit load so it can mature an appropriate number of bolls based on moisture availability.

Over the last eight days we have seen a general increase in many of our cotton pest. Cotton bollworm egg lays began to increase starting last Thursday and by Saturday some of our well watered cotton was up to 10,000 eggs per acre. By Sunday, August 4 we had counts up to 26,000 eggs per acre and on Monday counts ranged up to 69,900 eggs per acre in lush irrigated cotton. We do have some fields which have very little egg lay, but many have exceeded 7,000 eggs per acre. In most cases not many small larvae have been found, but his will change as more eggs hatch.

Eggs have been found at many locations on the plant. Eggs on the top surface of the leaf in the terminal have accounted for about 60% of the eggs found, but many have been found on the underside of the leaves.

Also eggs have been found on bracts of squares and bolls and on bloom tags. In some fields we have found over 60% of the eggs laid on the underside of the leaf. In some cases eggs found on the underside of the leaves have been cabbage looper eggs. Looper eggs are approximately the same size as bollworm eggs and can be difficult to differentiate. With the use of a hand lense, one can see that the ridges on a looper egg are much finer than a bollworm egg and a looper egg is flatter on the upper surface and appears to look like a deflated basketball. The bollworm egg is more oval shaped and often appears to set higher on the leaf surface than a looper egg.

Small and medium size bollworm larval counts have also increased and ranged up to 10,000 larvae per acre. With the increase in insect activity, predator counts have increased. Most fields are averaging around 18,000 key predators per acre. We generally feel it takes about 2 key predators per bollworm egg or small larvae to maintain a population below threshold; therefore 10,000 small larvae would require about 20,000 key predators to have an impact. The key predators we are currently finding are red cross beetles, damsel bugs (nabids), pirate bugs, big eyed bugs, lacewing larvae and spiders. We do not count lady beetles for bollworm management, since they are mainly in search of cotton aphids to eat.

Lygus bugs are on the increase in many area cotton fields. The nymphs of the Lygus bug tend to be a bright green with a small black spot in the center of the back. The cotton fleahopper nymphs look very similar to the Lygus nymphs and are often mistaken. The fleahopper nymphs are usually a lighter green color and lack the spot on the back.

The early instar Lygus nymphs are very difficult to tell from fleahopper, but they usually have dark antennae while fleahoppers are lighter in color. This week we have had counts of 1 Lygus per row foot. Our threshold for treatment is an average of 2 Lygus per 3 foot of row. The pyrethroids used for bollworm control will also control Lygus infestations.

Beet armyworm infestations remain scattered, but are generally on the increase. In several instances beet armyworms have been found feeding on bracts of squares, blooms and on small bolls with little evidence of foliage feeding normally associated with historic infestations. So far most infestations have remained below 10,000 per acre, but a few reports of 20,000 per acre have been noted. "Hits" (areas where foliage feeding is obvious) are on the increase in some fields but generally remain less than 1 per 100 feet of row.

Cotton aphids are increasing in many fields, with counts of 0 to 20 aphids per leaf commonly found. A few hot spots in fields have exceeded 500 aphids per leaf. Lady beetle larvae are abundant in many of the aphid infested fields and may be able to suppress populations until another pest in cotton has to be treated. Control can be achieved with Trimax, Furadan, Intruder and Centric. Intruder at 0.6 oz/a and Centric 40WG at 2 oz/a have provided up to 15 day control in Corpus Christi area tests.

Cabbage loopers as mentioned earlier are on the increase. So far foliage feeding is light. Many of the products used for beet armyworm control are also effective on loopers: such as Tracer, Steward, Confirm and Intrepid.

Spider mites have been found in a few area cotton fields. In most cases they cannot be associated with stress conditions. Both twospotted spider mites and carmine mites have been found. In drought stress situations we have seen these mites defoliate our cotton prematurely. We do have products that will control mites in cotton, but they can be very expensive. Lets hope our mite predators can hold these populations in check.

SORGHUM

Sorghum ranges from early bloom to soft dough.

Continue to scout daily for sorghum midge in blooming fields. Greenbug damage is increasing in some fields and should be monitored closely. The corn earworm egg lay (cotton bollworm) has also been occurring in sorghum. Scout sorghum as it completes bloom for both fall armyworm and corn earworm infestations. Infestations averaging one per head have been reported.

CORN

We are still collecting southwestern corn borer moths in area traps. Continue to scout corn for eggs and larvae. Early planted corn is at 100% dent and harvest should occur before significant lodging is encountered.

True armyworm and fall armyworm infestations have been reported in corn this past week. True armyworms can prematurely defoliate plants and fall armyworms can damage ears into the full dent stage.

Banks grass mites continue to increase in many fields. After the 100% dent stage is reached plants can tolerate very high populations without significant yield reduction.

 

Greg Cronholm, Extension Agent - IPM,
122 East 6th, P.O. Box 680
Plainview, TX. 79073-0680
806-291-5273
Ento. Dept. Website: http://entowww.tamu.edu
Dist. 2 Website: http://lubbock.tamu.edu
E-Mail: g-cronholm@tamu.edu

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