Web Site: http://entowww.tamu.edu
Vol. 30, No. 6

COTTON

Early planted cotton fields in the Hale Center - Cotton Center area now have bolls exceeding 1 inch in diameter; while late planted fields are just now starting to bloom. Overall, Lygus and fleahoppers remain below economic threshold in most fields. Lygus have been reported up to 1 to 2 per 3 row foot sampled. In past years we have used a threshold of an average of 2 lygus bugs per 3 row feet in the late square to early bloom stage. Treatment thresholds can vary up or down from the above stated threshold and must be coupled to square loss or small boll damage. If one is using individual plant inspections, the above Lygus count threshold could be converted to 12.5% plants infested for a 35,000 plants/a. population, 17% plants infested for a 50,000 plants/a. population or 25% plants infested for a 70,000 per acre plant population. If one is using number per acre, the threshold would be around 9,000 Lygus per acre.

Cotton bollworm activity has been on the increase in many area fields. Counts have ranged from 0 to 8,000 per acre. A few fields in Lubbock and southern Hale County have been reported to have small larval counts in the 30,000 to 40,000 per acre range. Our early season bollworm threshold can range from 5,000 to 12,000 per acre. We must consider many factors when making a decision to treat this early in the season. A lower threshold may be used if few or no beneficials are present in the field. A field like this may be one that was treated earlier for some other pest (ie. Lygus, aphids, boll weevils).

Beneficials can have a major impact on 1st, 2nd and 3rd instar bollworm larvae; therefore 8,000 small larvae per acre could be reduced to 2,000 per acre in a few days. Once larvae reach 3/8" in length the impact of beneficials drop significantly: therefore a population of 8,000 3/8 to ½ inch larvae will probably justify treatment. Also, environmental conditions can greatly impact survival of bollworm larvae. Rain, high humidity and cooler temperatures can increase bollworm survival. Dry, low humidity and high temperatures can have major influence to reduce survival rates. Secondary pest should always be considered. Treatment for early to mid season bollworms can lead to cotton aphid or beet armyworm outbreaks. If this is the case, bollworm treatment thresholds may be raised. Another factor to consider is cottons ability to compensate for early square or small boll loss.
The later we move into the growing season this ability to compensate declines; therefore a population of bollworms in mid-August has a greater potential for yield reduction than the same population occurring in mid-July.

Most of the corn earworm/cotton bollworm traps have now declined therefore we may see a decline in egg lays.

Beet armyworm trap collections have declined at several locations, but a few continued to collet 100 to 200 per 7 day period. Generally field infestations remain light. Cotton aphids continue to be found in many fields. Small colonies can be found hidden behind bracts and on occasional leaf.

CORN

Southwestern corn borer eggs began to be found in the Petersburg area on July 12 and in the Halfway and Earth areas on July 15 and 17. Trap collections of adult southwestern corn borers is on the increase at every trap location. Fields with 1st generation infestations have shown to be quiet variable. A field at Earth sampled on July 17 had only 2% emergence, while a field sampled at Halfway on July 16 had 21% emergence. The following is a prediction of emergence for the Earth location.

Banks grass mites continue to be the predominate mite in corn. If mites are present in any significant numbers it is a good idea to add a product to your southwestern corn borer treatments to help suppress or avoid a mite outbreak. The most common product used in recent years for mite suppression is dimethoate.

SORGHUM

Headworms have been reported infesting headed sorghum. The following table will help you to determine the economic threshold.

Economic injury levels based on number of corn
earworm and fall armyworm larvae per sorghum
grain head.

Control      Crop market value ($) per acre
cost ($)  ___________________________________________
per acre  100  125  150  175  200  225  250  275  300
_____________________________________________________
                 Number of headworms
6         1.5  1.2  1.0  0.9  0.8  0.7  0.6  0.6  0.5
8         2.0  1.6  1.3  1.1  1.0  0.9  0.8  0.8  0.7
10        2.5  2.0  1.6  1.4  1.2  1.1  1.0  1.0  0.9
12        3.0  2.4  1.9  1.7  1.5  1.4  1.3  1.2  1.1

Also remember that small fall armyworms and corn earworms in the head are targets for predators. In some of our insecticide treatment work over the years we have had up to 70% of the small larvae taken out by predators.

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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