Web Site: http://entowww.tamu.edu
Vol. 30, No. 11

COTTON
Many fields have now reached "full cut out" with very few white blooms left in the top of plants. Fields with limited water have shed most squares and small bolls as they have adjusted fruit loads to available water. These fields have most bolls safe from bollworm attack while a few bolls at the top of the plants remain vulnerable. Bollworms have a very difficult time becoming established in fields which have reached "full cut out" due to the lack of squares and blooms. Late planted fields or well watered cotton still have squares and blooms which contributes to higher levels of bollworm establishment. With this kind of variability between fields the threshold for bollworm larvae must also be variable. The fields at full cut out may have a threshold in the 12,000 to 18,000 larvae per acre range; while the late planted or fully irrigated cotton may still use the 8,000 to 10,000 larvae per acre threshold. Cotton bollworm egg lays have declined over the past few days and range from 0 to 50,000 per acre. Along with a drop in the egg lays the larval counts have also declined and have ranged from 0 to 18,000 per acre. We continue to hear reports of less than satisfactory control in some fields treated for bollworm by aerial application using pyrethroids. The reason for survivors is not known, since fields have been treated with adequate water rates to provide coverage on large size cotton. Larval survivors examined again this past week have all been cotton bollworms and not tobacco budworms. We could be seeing increased tolerance to pryrethroids as we move late into the bollworm control season.

This has been observed in the past (1980's), when we tested moths for toxicologist at the Department of Entomology at Texas A&M University. We may need to implement this program again if the problem continues.

Cotton aphid infestations continue to be highly variable. Some fields have declined to very low numbers, some have remained stable over the past week and some fields have increased. Fields with 25 to 50 aphids per leaf have had beneficials moving into the field to take advantage of a food source. Ladybeetle eggs and larvae are common as are lacewing larvae. Parasite "mummies" have been observed in several fields with higher aphid counts. Parasitized aphids have ranged from 1 to 5%. Once a field reaches 20% parasitism, it is unlikely you will have any aphids remaining in a short period of time. Don't spray a field based on the presence of honeydew on the cotton foliage. Aphids may have already crashed and the shiny leaves may be a remnant of the past. I continue to hear good reports on the performance of the new aphicide , Intruder.

Beet armyworm trap collections remained over 100 moths per week for this reporting period. Egg masses and newly hatched larvae have been common in a few area cotton fields. Several fields have been found with over 100,000 per acre, but many of these were recently hatched and survival to medium or large larvae may not occur. Treatment this late in the season will be based on the amount of fruit still susceptible. In general the beet armyworm is not as damaging to bolls as the cotton bollworm.

We often see instances where the beet armyworm larvae "nibble" on the larger bolls, but do not penetrate to the interior. Also it is hard to know how much damage is occurring to large bolls when the bracts are consumed by beet armyworms.

Lygus bugs continue to be found in area fields, but in most cases counts remain less than 2 per 3 row feet. Black spots on small bolls can still be found, but I am not sure how much yield reducing damage is occurring this late in the season.

Boll weevil treatments have continued by the Texas Boll Weevil Eradication Foundation. For the week ending August 18, 14,225 acres were treated in the Northen High Plains Zone for a total of 136,301 cumulative acres treated since the beginning of the season.

SORGHUM
Corn earworm and fall armyworm infestations ranged from 0/20 heads up to 30 per 20 heads sampled.

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

Sorghum midge infestations remain generally light. Continue to check late blooming fields, daily for this pest.

CORN
Corn harvest is underway for early planted and short season hybrids. Many fields are very close to being ready for harvest. In late planted corn, Banks grass mite populations remain very light. Some minor infestations of twospotted mites have been observed in a few area fields. Southwestern corn borer trap collections declined to a range of 11 to 104 moths per week in traps collected on August 21.

*** UPCOMING EVENT ***

 

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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