Silverleaf Whitefly Control in Cotton

The silverleaf whitefly (SLWF) is a devastating economic pest of cotton. A multi-county area surrounding Tifton, GA was heavily infested in 2016. In 2017, this infested area has spread over much of the 1.3 million acres of cotton planted in Georgia. In early to mid August of 2017, these SLWF infestations have spread throughout the Wiregrass area of southeastern Alabama.

The SLWF was first observed on cotton in Alabama in Mobile county in 1997. This pest has historically been associated with the more arid regions of cotton production such as California, Arizona, and the Rio Grande Valley of southern Texas. Major outbreaks occurred in those areas in 1992 and 1993.

SLWF has sucking mouthparts and their feeding is similar to aphids. This feeding will stunt plants and reduce their vigor. However, a more serious problem is their secretion of honeydew, which falls in lower parts of the plant. This would be lower leaves during the growing season but open bolls as the plants mature. A sooty mold grows in this honeydew, which will reduce the quality of the lint once cotton begins to open.

Heavy infestations of SLWF can cause premature defoliation. SLWF are not known to die off from a naturally occuring fungus like aphids. SLWF populations continue to increase until cotton is defoliated or until the leaves drop from SLWF feeding.

The first sign of a SLWF infestation will be the presence of whiteflies clustering around the plant terminal or underneath the terminal leaves. The adults will fly when disturbed, Population increases will be observed about two plus weeks after the first presence of adults. SLWF adults deposit eggs underneath the leaves. These eggs hatch into a crawler stage which finds a place under the leaf to begin feeding. This immature stage is then immobile until it develops into an adult. The total life cycle of the SLWF is 15-18 days, depending on the temperature.

Treatment decisions for SLWF can be made by examining for the presence or absence of immatures on the 5th main stem leaf below the terminal. Controls are recommended when 50% of the plants have immatures on the lower surface of this leaf. Immatures will appear oval, flattened, and yellowish in color. They can be separated from aphids by their flattened shape and the absence of appendages and movement.

Points to remember about SLWF as expressed by Dr. Phillip Roberts, Extension entomologist, UGA: Do not overreact but be careful to not underreact to this pest. You cannot get behind with controls and ever catch up. Try not to do anything to make the situation worse. Do not treat for other pests unless necessary. When controlling other pests, use the most selective insecticides on beneficial insects. Cotton is not safe from SLWD damage until the day it is defoliated for harvest. Growers should try to get to defoliation time with green leaves in the plant terminal with no honeydew present.

Rainfall may reduce the number of adults but will have no effect on the immature stage underneath leaves. The damage potential from the SLWF is greatest on late planted cotton (late May-June). This pest prefers hairy leaf or semi-hairy leaf varieties over smooth leaf ones. Hot and dry conditions are favorable for more rapid SLWF reproduction.

Controlling SLWF in 2017 will be very expensive and challenging due to the unavailability or short supply of most recommended controls. The most effective control can be achieved with the insect growth regulator (IGR) type insecticides Knack or Courier. Both work on the immature stage. Their activity is slow but they have long residual. It is advisable to wait 10-14 days after treatment before making opinions about benefits.

Other products that have activity on the SLWF are acetamiprid (Assail/Intruder), Venom, and Sivanto. Centric at high label rates will suppress the adult stage.

Stink Bugs Showing Up in Fields

Based on calls from consultants during the past seven days, most insect attention on cotton in Alabama has now shifted to the stink bug complex. This appears to be the appropriate thing to do since no other widespread destructive insect is being reported and a high number of stink bugs are being reported from all the major row crops. This began with wheat during the spring months. Stink bug numbers later shifted to corn. High numbers have been reported in recent weeks in peanuts, with increasing numbers being reported in both cotton and soybeans.

If we back up and review the situation since the end of the 2012 season, this is as expected. Stink bugs built high numbers on soybeans late last season resulting in a high level entering overwintering sites. This past winter was mild and we did not have the excessive high temperatures or extended drought this spring to limit a 2013 population build up.

This complex included both the brown and the southern green species. In the more southern counties within Alabama, the leaf footed bug is also in the mix. Leaf footed bug damage is identical to stink bug damage to cotton bolls. The important thing here is that, control wise, they are more like the brown stink bug. Phosphide insecticides do a much better job in controlling brown stink bugs and leaf footed bugs than do pyrethroids. Growers will need to keep this in mind as they select their chemical for treatment decisions. In Alabama, escape bollworms on Bollgard and Widestrike cotton varieties have not presented a big enough problem to select a pyrethroid over a phosphate for stink bug control. Field monitoring between July 20 and August 10 will determine if that trend holds true for the 2013 season.

In a few weeks, as we begin to make more stink bug control decisions in soybeans, we will have to work more with the pyrethroid chemistry to suppress the brown stink bugs in the complex. Research trials across the south point to bifenthrin as their superior pyrethroid for brown stink bugs in soybeans. We can improve the percent control by using the higher labeled rates.

Back to cotton, here is how we suggest making treatment decisions. First, select a minimum of 25 ten to twelve day old bolls that are still soft to the touch and can be crushed by hand. Select more bolls from at least two locations from larger fields. Crush these bolls and observe for internal injury. Note, it may make this process faster by first separating the bolls with external feeding signs from those that have none. First, crush the bolls with external feeding only and determine the percent that have internal injury. If a threshold is reached, then the remainder of the bolls with no external feeding signs will not need to be crushed. Internal damage may consist of one or more warts on the inside of the boll wall, damaged seed or stained lint. Second, the decision maker needs to know how long that particular field has been in the blooming stage. Most stink bug injury and loss is coming during weeks three though five or six of bloom. This is the period when most harvestable bolls are being set.

In Alabama, I suggest using a 10% internal damage threshold during weeks three though six of bloom. An insecticide application will usually suppress stink bug numbers for seven to ten days unless a field borders another untreated crop with high numbers of stink bugs. If has been my experience that stink bugs do not move rapidly across fields like plant bugs as they reinfest. The first four to ten rows adjacent to corn or peanuts seem to get most of the migration initially.

In our heaviest stink bugs years, cotton in the coastal plains of the southeast have required up to four applications. Under most conditions however, only two or three sprays may be warranted.

One last thing I will mention today is that, in the past, stink bugs seem to cause more internal boll damage in wet seasons than in dry seasons. That being the case, and unless the weather changes, we need to be extra cautious of stink bug damage to cotton in 2013.

Kudzu Bug Management and Control in Alabama Soybeans

Ron Smith, Extension Entomologist, Auburn University

The Kudzu bug has become a major economic pest of Alabama soybeans in certain fields throughout the state in recent weeks. Populations as high as 50 or more adult bugs per plant were observed in early June. Some of these fields now have 200 or more immature bugs per plant (late June). Calls are being received from growers and field men in recent days from all over the state.

Kudzu bugs are most highly attracted to early planted (April and early May) soybeans. Beans planted later, for example following wheat harvest, are much less attractive.

The primary question asked are when should soybeans be treated and what insecticide should be applied. The second part of the question is the easiest to answer. Most pyrethroid insecticides do a good job of controlling Kudzu bugs. Working thresholds have been previously established by entomologists in Georgia, North Carolina and South Carolina. For pre-flower vegetative beans a treatment threshold of five adults per plant is suggested. After flower, a threshold of one immature per sweep, with a sweep net, is recommended. As an alternative to sweep-net sampling, visual inspections of insect density lower in the canopy will suffice.  If immature kudzu bugs are easily and repeatedly found on the leaf petioles and/or main stems, treatment is likely warranted. However, these threshold guides may be modified slightly based on the number of egg masses that are continuing to hatch.

Kudzu bugs have two generations per season on soybeans. Adults move from Kudzu to early planted soybeans in the spring, deposit egg masses and eventually die. The immatures then hatch and eventually become adults after about six weeks and begin to deposit eggs for the next generation.

A limited number of Kudzu bugs may appear in beans season long. The most efficient and economic use of insecticides occurs when an application is made when the majority of the population in each generation is in the immature stage. Some fields have already exceeded treatment threshold and will likely require two or more sprays during the 2013 season. Fields with lower populations may be able to wait until mid-July or later for a treatment. Only one application may be needed in these fields during the 2013 season. 

Applications made when a high number of unhatched egg masses are present may have to be repeated within one to two weeks. Our goal should be to strategically time these insecticide applications for maximum effectiveness. Treating soybeans repeatedly at close intervals has not resulted in yield increases over fewer well timed applications. The key point is for growers and field men to focus on the peaks of immature Kudzu bugs as we move through the 2013 season.

There will be no way to economically prevent yield losses to Kudzu bugs and minimize inputs without monitoring or scouting soybeans weekly just as we have done in other row crops for decades. Kudzu bugs are not the end of the world for soybean production in Alabama but they do create a new day. Pictures of adult and immatures are available on Ron Smith’s blog http://alabama-insects.blogspot.com/. Basic Kudzu bug information can be found at http://www.clemson.edu/extension/Kudzubugs/index.html. Updates on the Kudzu bug status will be posted on the www.alabamacrops.com website. The Extension Soybean IPM guide has recommendations for Kudzu bugs on page six http://www.aces.edu/pubs/docs/I/IPM-0413/IPM-0413.pdf. Also, there is a podcast now available here http://agfax.com/2013/07/01/first-time-with-kudzu-bugs-listen-up/.

Adults

Egg Mass

Weather Conditions and Pest Control

First we will give an overview of weather conditions, especially since this may be impacting some of our insect and pest control decisions in the coming days. After a good moisture and rainfall pattern of about 10-14 days ago, our crops have reached a hot-drought stressed condition at present. The situation is worse in the northern area of the state where less rainfall fell during the last thunderstorm period. I saw corn wilted bad in the Tennessee Valley on Tuesday (June 19).

This droughty situation could well impact spray decisions with pests such as aphids and s. mites in the immediate days ahead. Aphids are building state wide and drought stress plants are where I am more suggestive for chemical controls instead of waiting for the natural fungus.

Tarnished Plant Bug adults are also being reported from some fields from the Tennessee line in the north to the Florida line in the south. Square retention is dropping, especially in fields in South Alabama that are a couple of weeks into bloom – these would be early-mid April planted cotton. Also in these some fields, adult brown stink bugs are being reported. We know from past years what stink bugs do to small thumb sized bolls when no larger ones are present.

If present in cotton, stink bugs will feed on small bolls to develop. Knowing this impacts the chemical that we may want to choose for TPB control. It needs to be a product that also controls or highly suppresses Brown Stink Bugs. The best options here would be Bidrin or a high rate of bifenthrin. Aphids in the picture would further complicate the chemical selected. Of the neonic type products, Centric might be the best choice for Tarnished Plant Bug adults, Brown Stink Bugs and aphids.

Three-Cornered Alfalfa Hopper damage is still evident in cotton, in reddish stunted plants that have a girdled and swollen area around the main stem. However, this damage is old now and most plants are too tough for main stem girdling by the Three-Cornered Alfalfa Hopper.

The biggest insect news of the week in Alabama was the finding of the Kudzu bug in soybeans in Cherokee County, Alabama on June 21. The Kudzu bug had been found in about 25 counties on Kudzu but this was the first find on soybeans. Alabama growers will want to lean heavily on recent research conducted in Georgia, South Carolina, and North Carolina on this new envasive pest. We need to beef up our scouting on soybeans for this pest – especially the immature stage.

Kudzu Bug Found Infesting Alabama Soybeans

The kudzu bug was detected this week in 2 soybean fields in Cherokee county which borders on Georgia where the pest was first detected in the Athens/Atlanta area in 2009. The pest has spread rapidly since it was first detected and now has been found in 7 SE states. The kudzu bug had been found previously on kudzu in 25 Alabama counties but this is the first report on soybeans. Economic yield losses by soybeans due to kudzu bug feeding have been reported in Georgia. (The following information was taken from the 2012 Georgia Soybean Production Guide)  Adult kudzu bugs are oval shaped,  about ¼ inch in diameter, and greenish brown in color. Eggs are laid in double-rowed batches of 35-50 eggs and are white in color. Nymphs are also oval shaped and are light green to brown in color and have numerous setae/hairs. Both adults and nymphs are most commonly seen on plant stems using their sucking mouthparts  to feed on plant sap. The effects of kudzu bug feeding on soybeans is similar to drought. Excessive feeding weakens and stresses the plant which can result in fewer pods per plant, fewer seeds per pod, and reduced  seed size.  Overwintering adults survive under pine bark and ground debris . Key reproductive hosts of kudzu bug include kudzu, wisteria , clover and soybeans. Adults begin laying eggs on kudzu shoots in  mid-April and continue laying eggs on kudzu for several weeks. Time required to reach the adult stage is about 6-8 weeks. These new adults then disperse to soybeans and other reproductive hosts beginning in mid-June and continuing thru mid-July. Soybeans become attractive to kudzu bug adults when plants are 8-10 inches tall. Early planted soybeans appear to be at greater risk for kudzu bug infestation compared with later planted soybeans. Adults will begin laying eggs on the underside of soybean leaves and a generation requiring about 6 weeks will be completed on soybeans. Initial field invasions tend to be more concentrated on field margins but will eventually spread throughout the field. In many situations we will begin to see immature kudzu bugs in soybeans at about the R2-R3 stage. Kudzu bugs can be scouted using a 15-inch diameter sweep net. Kudzu bug populations can be extremely high. Georgia entomologists are suggesting a threshold of one immature kudzu bug per sweep. This suggested threshold is based on 2011 field trials where a single properly timed insecticide application preserved soybean yield. If insecticides are applied when adults are still actively migrating from kudzu to soybeans (late June and early-mid July); additional applications may be needed. Research is ongoing to verify and refine management and treatment thresholds for kudzu bugs in soybean. Multiple classes of insecticides have shown activity on kudzu bugs. Insecticide treatments containing bifenthrin, cyhalothrin, zeta-cypermethrin, carbaryl, or acephate provided greater than 80 percent control 2-5 days after treatment.

Immature Grasshoppers in Winter Cover Wheat

Cotton planting is underway in a significant way in some south Alabama counties. A question was received today from that area about what to do with the grasshoppers in winter cover wheat that is currently being burned down prior to planting cotton. Immature grasshoppers are present at thousands per acre in the wheat. My recommendation would be to control these grasshoppers at the same time wheat is being burned down or prior to the time the cotton begins to emerge. They pose a significant risk to stands if allowed to remain in fields. Based on our research of several years ago, immature grasshoppers can be easily controlled with a low-to-mid range rate of most any insecticide labeled for cotton. The pyrethroids do an excellent job and are very economical. Adding 1 oz. of Dimilin per acre to the mix would provide residual control of immatures for weeks down the road. Since we are still early in the spring, there could be some additional migration into fields from hedgerows and field borders. The problem with waiting until later to make an application is eventually these immature grasshoppers will become adults, which is much more difficult to control.

True Armyworms Spotted in Early April

True Armyworms were reported on April 2^nd feeding on rye near the Wiregrass Research Station (near the Headland, AL airport), in Henry County. This insect had previously been reported from the Coastal Bend of Texas to South Georgia and as far north as Kentucky. The larvae feed mostly at night and may not be found in daylight hours until digging into the soil surface debris. The larvae vary from green to brown with lighter stripes on their sides and back. In some ways they look similar to Fall armyworms.

These caterpillars can cause extensive damage below the crop canopy before they are detected. Controls are suggested when 4 to 5 larvae per square foot are found and feeding is heavy on the lower leaves. It is important to protect the flag leaf.

Most all insecticides labeled for small grains will provide adequate control. They are not as hard to kill as fall armyworms in cotton. However, good coverage is important, especially when making applications by air.