Northwest Plains Pest Management News Vol XI Issue 13

The harvest season is off to a rapid start as silage choppers are rolling in area corn. Conditions are very good and harvest has not been impeded by weather making harvest quick and efficient. 

The irrigation termination decision making process in corn continues. Assuming an adequate crop condition we normally say that once the starch line has reached 50%, irrigation can be terminated with no detrimental affect. The key to this crop stage irrigation termination point is it assumes a full profile of moisture from which the plant will pull moisture to finish filling grain. If the soil profile is not near capacity at 50% starch line, additional moisture in the form of irrigation or rainfall will be required to finish the crop. With sprinkler and drip irrigation systems we have the capability to tailor late irrigation applications to specific crop needs. Early irrigation termination can significantly reduce corn yield. The starch line is an indicator of crop maturity, corn kernels mature from the outward tip inward toward the cob. A distinct color separation is visible on each kernel and moves down the kernel as it fills. The starch line is easily seen by breaking the ear in half and viewing the cross section. 

Headworm activity in sorghum has really picked up, many observations have revealed headworm numbers 4X the established economic threshold. Current infestation are near 75% fall armyworm (FAW) and 25% corn ear worm. What appears to be happening is the majority of the FAW are hanging out in the foliage until some grain formation appears then they are moving to the head to feed on developing grain. In this scenario fields with few worms in the head a few days ago could be infested with large worms with large appetites very quickly; large larvae consume 83 percent of the total grain consumed during larval development. Treating the worms before they move to the head will not be as effective simply due to the fact that larvae in the heads are directly exposed to the insecticide. A complicating factor in managing headworms is the presence of spider mites. If mites are established then product selection to suppress headworms should be carefully considered as many of the traditional and often cheaper options may flare the mites which could then devastate the sorghum. In situations where mites are present at low levels the use of Belt should provide good headworm control while not flaring mites. If mites are well established then Comite or Onager should be considered as tank mix partners to suppress the mites. Large numbers of spider mites occurring early in kernel development can reduce the ability of sorghum plants to make and fill grain. After kernels reach hard dough, grain is not affected. Additionally, if spider mites are very abundant sorghum plants will have much weaker stalks which and may lodge, which can result in severe harvest losses. 

FAW in sorghum head

Bollworm moth activity and egg lay has picked up over the last few days. Diligent scouting will be necessary to identify fields with economic levels of bollworms. The decision to treat for bollworm should be based on number of larvae/acre, larvae size, and the maturity of the crop. Most of the area cotton is late and still has a lot of squares and small tender bolls which very suitable for larval development. Most of the small fruit has little if any chance to make a harvestable boll but larvae could become established on this then move to more mature bolls as they gain the ability to penetrate larger fruit. Generally we consider bolls which have gained 450 heat units after bloom to be safe from bollworm damage. The late crop makes determination of which bolls are worth protecting much more difficult; we will likely be tempted to protect a much later boll than what we normally would. This adds significant risk associated with getting a positive return on an insecticide application since the later bolls have less time and probability to mature. 

Loopers are common in many cotton fields, they feed on foliage making small holes in the leaves. Very high populations could cause excessive loss of leaf surface area but I have not observed any infestations near that level. There is no established treatment threshold in Texas but NCSU suggests “ If the defoliation reaches 25 percent and a significant number of bolls that the producer expects to harvest are still filling out, treatment may be advised. However, remedial sprays may have only marginal effect on the more common soybean looper.” To round out the current Lepidopteron spectrum beet armyworm, yellow striped armyworm and Arctiid moths, eggs and larvae have also been observed in area cotton. Beet armyworms at present infestations are at tolerant levels but what makes this pest more concerning than other foliage feeders is it may transition to feeding on small bolls. 

Looper and feeding damage to cotton leaf

Late planted corn has been and continues to be very attractive to lepidopteron pests. FAW and southwestern corn borer have been observed in alarming numbers in late planted non-Bt corn. FAW will readily feed on emerging silk which can inhibit pollination. In extreme cases I have seen heavy FAW pressure reduce pollination by more than 90%. Any late planted corn should be carefully monitored for these pests.

Southwestern corn borer larva

Northwest Plains Pest Management News Vol XI Issue 12

Scattered thunderstorms continue to provide much needed moisture to thirsty crops in their paths. Some of the storms contained hail which has caused some crop damage, but for the most part, the benefits of the moisture out weigh losses due to hail. Much of the earlier planted corn is in full dent while the latest planted corn has yet to tassel. Cotton is at peak bloom with most fields between 5  to 6.5 nodes above uppermost white flower (NAWF). Grain sorghum is responding very well to additional moisture from recent storms. Field maturities range from milk stage to those still growing vegetative. 

Grain sorghum should be regularly inspected for headworms from head emergence until hard dough. Estimating the economic injury level for headworms is complicated because the potential yield loss varies with the size of the larvae. That is why it is necessary to record the number of small (up to 1⁄4 inch), medium-size (¼ to ½ inch long) and large (1/2 inch long or longer) headworms. Small larvae  consume very little grain (about 10 percent of the total) and about 80 percent of them die in this stage. Therefore, small larvae should not be considered in determining the economic injury level. If most headworms are this size, sample the field again in 3 to 4 days. About 19 percent of medium-size larvae  survive beyond this stage. Thus, the potential grain loss from medium-size larvae is only 19 percent of the potential loss from large larvae. Most corn earworm larvae larger than ½ inch will survive to complete development, and these large larvae are most damaging; they consume 83 percent of the total grain consumed during larval development. If most of the larvae are larger than ¼ inch, determine which size (medium size or large) is most common and use the corresponding threshold to make treatment decisions. An Android based threshold calculator can be found at the Google Play Store; http://goo.gl/8mXvv . We also have a web app for other operating systems which can be accessed at http://goo.gl/5k7ZtU .

The beat-bucket technique is the best way to estimate the number of headworms in sorghum. Shake sorghum grain heads vigorously into a 2 to 5 gallon plastic bucket (a small white office trash can works well), then count the caterpillars in the bucket. For easy math I like to work with sets of 10; where I shake ten random heads as I walk down the row then I count and evaluate the size of the larvae. If more heads are sampled in a set there may be too much “trash” in the bucket to efficiently make counts. Record the number of small, medium  and large  headworms found in the samples. Then use the threshold appropriate for the size of the majority of the headworms. Using the calculator mentioned earlier, where control cost is $15/ac and grain value is $8/CWT an insecticide application should be considered if 19 medium (1/4 to 1/2 inch) or 4 large (>1/2 inch) worms are present per 10 heads (based on 50,000 heads/ac).

Beat bucket sampling, TAMU photo

Lots of moth activity has been observed in area cotton, most has actually been smartweed borer but the number of bollworm moths has picked up recently.  Adults are yellowish brown moths with a wing span of approximately 1.5 inches; considerably larger than the smart weed borer.   Eggs are about the size of a pin head, white and somewhat domed shaped with ridges running from top to bottom.  Eggs can be easily confused with looper eggs which are flattened on top. Larvae range from 1/16 to 1 5/8 inches long depending on age.  They are variable in color including yellowish, greenish, or brownish forms with a tan to brown head.  Black bumps with a protruding spine are uniformly distributed over the body. Some may be conspicuously striped. Newly hatched larvae feed on tender vegetation for a short period after emergence.  This vegetative feeding is rarely damaging.  Larvae then move to and feed on squares and bolls.  This direct fruit feeding, often times, will result in economic loss depending on the number of larvae present. Treatment may be justified in conventional cotton if 10,000 small (1/4 inch or less) larvae per acre are present.  If larvae are 3/8 inch or more in length then treatment will likely be justified if 5,000 or more larvae per acre are present.  Treatment decisions in Bt cotton should not be made based on small larvae since some feeding must occur before larvae are controlled. Treatment of Bt cotton may be justified if 5,000 or more medium sized larvae (3/8 to ½ inch) per acre are present and square and/or boll damage is observed. 

Cotton bollworm moth on cotton bloom.

Spider mites persist in many corn fields in varying degrees. Some populations have been held in check by miticides and beneficials while others continue to grow. A miticides residual activity has certainly been tested this year. Some fields have not had beneficials in great enough densities to help suppress mites for an extended period. .  Most yield loss is a result of feeding damage at or above the ear leaf.  Yield loss is a result of reduced grain fill, premature dry-down, and weaker stalks which may cause lodging.  Once corn is fully dented mites will not likely impact grain development but could still impact stalk strength.

Spider mite pressure in corn

2013 Boll Weevil Eradication Changes For NWP Zone

The Commissioner of Agriculture has set the 2013 assessment rate for the NWP Zone at $1 per dryland acre and $2 per irrigated acre. As part of the rate reduction the failed acre credit has been eliminated. So what does this mean? All planted acres of cotton will be assessed. For more information contact the Foundation at 1-800-687-1212 or log on to www.txbollweevil.org. 

Sorghum Headworm Calculator

Treatment thresholds for sorghum headworms are dynamic based on grain value, cost of control, and infestation levels. We have developed a sorghum headworm calculator "app" which is available on the Google Play Store at http://goo.gl/8mXvv  The app can also be found by searching for sorghum in the store. The app will run on any android device with an OS of 2.3 or above. We also have a web app which can be accessed at http://goo.gl/5k7ZtU. The Android app calculates larvae/10 heads while the web app calculates larvae/head.

Northwest Plains Pest Management News Vol XI Issue 11

Last weeks isolated thunder storms carried some baggage; pockets of hail destroyed some area crops. The speed at which moisture has disappeared is a testament to the current moisture demands of crops (and

weeds). Corn continues develop at a good pace; some corn is near dent while other fields are growing vigorously. Moisture demands remain near maximum in corn from tassel to milk stage but begin to decline as the crop transitions from milk to the dough stage and continue to decline at a fairly rapid pace through maturity. Much of the area cotton crop is in full bloom and is at or near maximum moisture demand. Irrigation should be carefully managed to promote earliness and maintain fruit load; many times this is walking a fine line. Lower amounts and more frequent irrigation applications will allow producers to speed maturity and maintain yield; adjustments in irrigation frequency and amount should be based on individual field conditions. Much of the grain sorghum is also at or near peak moisture demand which is from boot to heading. Using a moisture probe to monitor soil moisture levels has become futile in many fields with limited irrigation capacity as the probe cannot penetrate the soil. 

Weed management has been a continual battle; weed resistance to herbicides, primarily glyphosate resistant pigweed, is a huge concern. Every effort should be made to remove suspected resistant weeds from the production system. Now through harvest will be a good time to make a few notes on field specific weed issues to refer back to as weed management plans for 2014 are developed. 

Pigweed killed by glyphosate on right and an unaffected potentially resistant pigweed on left

Insect pressure remains very light to non-existent in cotton but verticillium wilt has really intensified. Verticillium wilt is a soil born fungus that cause plants to wilt but does not cause root rot. The pathogen in affect plugs up vascular tissue preventing the translocation of moisture. Stalks of plants can be cut longitudinally and inspected for brown streaking for a quick in field diagnosis. There are no curative treatment for verticillium wilt in cotton, the key management tactic is to plant resistant/tolerant varieties. So, as with weed management make some field notes on “vert” pressure that can be used to help make variety planting decisions next year.

"Vert" symptoms on leaf.

Spider mite pressure remains high in many corn fields and miticide applications are on going. Mite suppression has been good in some fields while others have had to be retreated. Coverage is critical to maximize miticide efficacy. Increased total volume of spray will provide better coverage and penetration into a dense canopy, 5 gallons per acre should be considered minimum. A much higher incidence of spider mite destroyers (Stethorus) have been observed feeding in in mite colonies recently. The spider mite destroyer is a very small beetle in the lady beetle family (Coccinellidae). The beetle is about 1/16 inch long and shinny black; the larvae are gray to brown with a miniature alligator type appearance (minus the teeth :-) ). Both the adult and larval forms are key predators of mites and will help stabilize mite populations. Mite management tactics should exploit these natural enemies; avoid pesticide applications which will destroy your partners in mite management.

Spider mite destroyer (Stethorus) adult left and larva right

An occasional sorghum headworm has been observed in area sorghum. As grain sorghum transitions from vegetative growth to heading whorl feeding pests will shift to feed in developing heads. Corn earworm and fall armyworm commonly referred to as the headworm complex in grain sorghum, rank as the third most damaging insect pests of sorghum in the United States.   Treatment thresholds for sorghum headworms are dynamic based on grain value, cost of control, and infestation levels. We have developed a sorghum headworm calculator "app" which is available on the Google Play Store at http://goo.gl/8mXvv  The app can also be found by searching for sorghum in the store. The app will run on any android device with an OS of 2.3 or above. Once the app is installed no internet connection is needed. We also have a web app for other operating systems which can be accessed at http://goo.gl/5k7ZtU. The web app will require an internet connection to work. The Android app calculates larvae/10 heads while the web app calculates larvae/head.

Some corn damaged by hail in late June is not pollinating adequately simply due to the lack of pollen production. Injury to the small developing tassel in late June has caused some tassels to be completely bare. 

Injured developing tassel left, barren tassel right

Northwest Plains Pest Management News Vol XI Issue 10

Rainfall blessed portions of the NWP area on the last day of July; NOAA weather stations in Friona and Muleshoe recorded .5 and 1.78 inches respectively. Individual reports in excess of 3 inches were also received. The area corn crop continues to progress very well with a wide range of maturities from less than two feet tall to blister stage. The cotton crop continues to play catch up, but is developing at a good pace. Yield potential is fair to good for the most part. Grain sorghum, as with corn has a wide range of maturities ranging from vegetative to heading and blooming. Most fields are on track to fully mature but late planted fields could be hurt by frost especially if development is slowed by stress. 

Corn pest pressure has increased, in addition to existing spider mite issues Southwestern corn borer (SWCB) activity has dramatically  increased this week; trap captures are up 10 fold compared to last week. Yield losses from SWCB may occur as a direct result of stalk and or ear shank feeding, as well as lodging.

Bt hybrids are very effective in controlling Southwestern corn borer but required non-Bt refuge and other non-Bt corn will have to be managed traditionally. The established economic threshold for second generation Southwestern corn borer is when 20% of plants are infested with eggs or small larvae. Timing is critical when making an insecticide application; insecticides must be applied prior to larvae boring into the stalk to be effective. Small larvae will feed on leaves, ear shoots, husks, and silk for about 5 to 10 days before tunneling into the stalk or ear shank and continuing to feed. Insecticides should be selected carefully; some are harsh on beneficial arthropods and may cause a secondary outbreak of spider mites.  

Spider mites persist in many fields while others remain nearly mite free. Many fields with established mite

populations have exceeded treatment threshold and have been treated. Current miticides are slower to fully suppress mites than what we see when treating most other insect pests. At 7 DAT it may look like a miticide has had no impact at the field level since there may actually be more mites present than before it was treated. In research conducted locally, labeled miticides averaged  about 55% control 7 days after treatment. This is not to say that there are half as many mites in the treated plots than before treatment because mites have continued to develop, but, and it is a big but, the plots treated with miticides have reduced mite pressure compared to that observed in the untreated plots. Remember we want to minimize mite colonization of the ear leaf.  

Fall armyworm have been observed feeding in non-Bt corn in varying degrees. Larvae have been observed feeding in silk, behind ears, and behind leaf collars. There is no established treatment threshold for FAW in corn but recent research confirms they can consume a significant amount of grain when feeding in the middle of the ear in addition to ear losses due to ear shank feeding.  There is a detailed presentation by Pat Porter which discusses potential grain loss due to FAW feeding in corn, it can be viewed at http://goo.gl/X9jy4O

FAW behind ear leaf

Cotton pests remain quiet even though I observed a “lost” bollworm feeding in a square this week. In corn growing areas, corn continues to be the favored host plant for bollworm/corn earworm at this stage. With recent precipitation plant growth should be closely monitored as we may not have enough boll load at this point to prevent excessive vegetative growth. In fields with good moisture and a later developing boll load a plant growth regulator may be necessary to keep cotton development on track. 

Sunflower head moth larvae have been observed feeding in pre-bloom sunflowers which may be an indication of heavy infestations once blooming has commenced. The head moth, is the single most important sunflower pest in Texas. Sunflower moth infestations are usually heaviest early in the growing season, with another smaller moth flight possible later in the season. The adult is a small, slender, silver-to-buff gray moth about 1⁄2 inch long. It is most often seen resting on sunflower heads during the blooming period, especially in early morning and early evening. Moths are highly attracted to plants beginning to bloom. Nearly 80 percent of the eggs are laid on the plant within 4 to 7 days after buds begin to open. Eggs hatch in 24 to 72 hours. Newly hatched larvae are yellowish. Mature larvae are brown with four yellowish-green to cream colored longitudinal stripes. For the first 5 to 6 days after hatching, young larvae are relatively exposed as they feed on pollen and floral parts on the flower surface. Insecticide applications should target the very early bloom period when yellow ray petals are visible.

Sunflower head moth larva feeding in bud.

Heat Unit Accumulation and Current Crop Moisture Demands

DD 60 based on May 1 planting date