Early August Insect Update

It has been a number of days since we last reported on Alabama insects. So what has been happening? First of all, August has been dominated early-on with little insect activity other than the bug complex in cotton. Second has been the weather, we had sun yesterday, August 19, for the first time in about 10 days. During this period, rainfall has been measured in inches varying from low single figures to double digits, depending on the location. Up to 4 inches in a 24 hour period has been common. This has resulted in bridges and roadways being washed out and public schools closing during the beginning of the fall term. Agriculturally wise, sprayers have been unable to get into fields and aerial applicators are over booked. Fortunately, insects have overall been low with just a few exceptions. The bug complex has been over threshold in many but not all cotton fields. In the past few days the caterpillar complex has built to damaging levels in soybeans. Some fields have been sprayed by plane for the lep complex, primarily loopers and velvetbean caterpillars. The heaviest infested fields are those where growers just preventatively added a pyrethroid when they were applying a fungicide.

It has been my experience in research plots that an application of a pyrethroid just prior to an infestation of foliage feeding caterpillars is like throwing gasoline on a fire. We usually see much higher numbers of soybean loopers where a pyrethroid application has been made within the previous 10-14 days. My advice to growers is that if they feel they must add something to their fungicide, just add 2 or 3 ounces of a product like Dimilin which does not disrupt the beneficial insects.

Once we have a damaging level of foliage feeders the first thing we need to do is to quantify the species present and the numbers. Five to seven caterpillars per foot of row will usually result in 30% or more foliage loss and therefore require controls. Treatment thresholds for sweep nets on drill beans are not quite as well defined. However, 2 to 5 per sweep would likely require controls. As to species, velvetbean, green cloverworms, corn earworms (podworms) and stink bugs can all be controlled with a pyrethroid. However, if many soybean loopers are in the mix, then one of the newer lep materials will be required. These are, in chemical alphabetical order: Belt, at 2-3 oz.; Steward at 7 oz.; Intrepid at 4-6 oz.; Prevathon at 18-20 oz.; tracer or Blackhawk at 1.5-2 oz. per acre.

One additional thing should be added about soybean looper control, especially if application is by air. Looper eggs are deposited on the lower leaves of the plant, therefore they infest the plant deep within the canopy. As the larvae mature they feed upward through the canopy. In order for any of the newer chemistry to be effective, the leaf containing the droplet has to be eaten. Therefore, it may take several days to fully suppress a looper population. It has been my experience that the surviving  larvae behind application will be early instar larvae found lower in the canopy. Most of these looper insecticides are very rainfast and have long residual on the leaves, so don’t panic if you see a few small loopers behind an application.

I will be on research farms for the next several days and will get back soon if we see or hear of damaging levels of insects developing.

Update for the Week of September 9

As we observed and stated last week, soybeans in Alabama are experiencing the most widespread outbreak of foliage feeding insects of the past 41 seasons. This outbreak has been going on for about three weeks or more. However, some growers are just now discovering the situation. This has led to the most calls and questions that Dr. Tim Reed and I have ever received during one week. I will attempt to summarize the questions and what our responses have been.

Most calls begin with – “I have worms in my soybeans, when do I need to treat and what insecticide do I need to use?”

First of all, in most all fields we are dealing with a mix of soybean loopers (SL), velvetbean caterpillars (VBC), and green cloverworms (GCW). Loopers are statewide, VBC are a significant part of the mix in south and central Alabama while GCW are a large part of the mix in northern areas of the state. Loopers are resistant to pyrethroids, Lannate and all of the older chemistry. Since they are part of the mix statewide, we must go to the newer chemistry (in alphabetical order): Belt 3 oz.; Blackhawk (Tracer) 2 oz.; Intrepid 4-8 oz.; or Steward 7 oz. Prices for Belt, Blackhawk and Steward will be somewhere between $15 and $20 per acre. Intrepid will range from about $7 to $14, depending on the rate used. The 4 oz. rate has been what most growers have chosen due to economics. However, where significant foliage loss has already occurred and worm numbers are high, this 4 oz. rate is not adequate. At least 5 or 6 oz. of Intrepid will be needed.

In addition to worms, most all soybean fields have some level of stink bugs present. None of the worm materials will control stink bugs. Therefore, a pyrethroid or acephate (Orthene or generic) at 0.75 lb./ai must be added. This rate of acephate makes pyrethroids the most economic choice. The majority of our stink bugs are the green or southern green species, which pyrethroids control very well.

Now back to what a threshold is on foliage loss. Depending on the stage of beans, our threshold is 20-30% foliage loss. That does not mean that we wait for that level before treating. We treat in advance when we find worm numbers that will give that level of loss. Also, we must allow 4-5 days for products like Intrepid to control the worms. However, foliage consumption will normally end much sooner. Big factors, which are seldom mentioned in discussing foliage loss thresholds in soybeans, are the amount of moisture available to the crop and the reproductive stage of the beans. Soybeans can compensate at a much higher level when soil moisture is available and we have that statewide at present. Also, soybeans will replace lost foliage when they are still in the blooming stage.

How many worms does it take to cause 20-30% foliage loss? In traditional row beans, where a drop cloth can be used, somewhere between 4 and 8 larvae per row foot will give 20-30% foliage loss. The size of the beans is also a variable here. Due to the good moisture in August, many of our beans are waist high and have lots of foliage. Many of our beans in 2012 are drilled. Therefore, a sweep net is needed to get a measure of worm numbers. I suggest taking 10 sweep samples. Some states recommend treatment when about one larva per sweep is found. I have found in 2012 that it takes about 3 or 4 worms per sweep to cause 20-30% foliage loss. Another factor to consider is how long the worm infestation has been ongoing. In fields I have monitored, the answer is three or more weeks. New worms just keep hatching, so where a subthreshold has been present for 15-20 days, much of the lower canopy has already been consumed by the worms. In this situation a 10% foliage loss can turn into a 30-40% loss in 7 days.

In summary, I feel that our Extension educational program on soybean insects has been very inadequate and we promise to do better beginning with winter meetings. However, growers must also do their part in managing insects in soybeans, especially when they are worth $17-18 per bushel. We do not know what level of insect pressure 2013 will present, but if we plan to stay on top of the insect situation, soybeans will need to be monitored by a trained or experienced person at least weekly during the season, just like we have done in cotton for the last 60 years.

Update for the Week of August 19

Our April-planted cotton is beginning to open, and has varying levels of boll rot due to the weather the past 7-14 days. This same weather pattern of frequent thunderstorms and overcast conditions has been ideal for the spread of leaf spot diseases in out late planted cotton.

Insects have been light-to-nonexistent in recent days. There are a few plant bugs present and stink bug numbers have increased in some fields. I am not sure if either are at damaging levels, especially the plant bugs.

I believe we could safely say that leaf spot diseases are potentially more important than insects for the remainder of the season.

Growers who have peanuts or soybeans should monitor these crops carefully for the remainder of the season. Peanuts are attractive to a number of foliage feeding insects – including loopers, fall armyworms, bollworms, budworms, green cloverworms, velvet bean caterpillars and cutworms. Two peanut fields in Monroe County were identified last week with a high infestation of the garden fleahopper. To my knowledge this is the first time for this insect on peanuts. I am not sure what kind of damage potential they present. However, in cotton this pest can cause extensive foliage damage by leaving all leaves with stippling type feeling.

This same type of damage in peanuts would seem to be just as economic as a foliar disease.

Soybeans would be susceptible to damage from all the leps mentioned under peanuts plus the pod feeders – podworms and stink bugs. Many of our beans are late, planted behind wheat, and were just in full bloom the past 10 days. These beans will be susceptible to insect injury for weeks ahead. Only by scouting will growers know when economic insect losses are occurring and when controls are needed. We already have some fields in Baldwin County with damaging levels of soybean loopers. Foliage loss was as high as 35% last week when I made surveys in that area. Soybeans will be the last crop that stink bugs are attracted to this season. Even though it has been a light stink bug season, if they all accumulate in soybeans late season, controls will likely be needed.

I have heard little from the Kudzu bug on soybeans after finding them in the northeast counties of Cherokee and Cleburne back in July. Follow up surveys are needed in that area whenever time permits.

As the season winds down we will get back with further updates as new information becomes available and the situation changes.

Update for the Week of August 12

Last week was rather quiet insect wise on cotton. Many areas received thunderstorms throughout the past 7 days. The comments that I will make today are based on observations made in the field from several different areas of the state last week.

The first point is when to back off of stink bug controls. Our early April cotton is beyond the eighth or ninth week of bloom with few to no 10-12 day old bolls remaining. In fact, my test plots of PHY 375 planted April 9 had several open bolls per plant early last week. Even with cotton that still has a few 10-12 day old bolls remaining, stink bug numbers are so low in most fields that a stink bug threshold could never be reached. I would not be concerned at all with 10-20% internal damage as cotton is maturing out and beginning to open. For those who would be spraying with ground equipment, and that would consist of the majority of growers in Alabama, a ground rig going through mature cotton would destroy far more good bolls than the few smaller bolls near the top of the plant that stink bugs might injure.

Spider mites populations held steady last week but did not seem to increase, likely due to the frequent thunderstorm occurrence. I would just keep an eye on them and delay treatment decision as long as the current weather pattern holds.

One of the heaviest tobacco budworm flights seen in several years has been ongoing in the southern counties. Moths, eggs, and small larvae have occurred in high numbers from Dothan in the southeast to Fairhope in the southwest. This will have no impact on cotton with Bollgard or WideStrike technology. However, conventional varieties are a different story. I was in research plots of conventional cotton with no insect technology at Fairhope, AL on August 7 and found 32% worm square damage with 9% of the squares containing live larvae. Who says the technology has less value than it once did? In the old days, what would we do under this level of pressure, with thunderstorms occurring every afternoon?

Growers that may be impacted by this budworm pressure are soybean and peanut producers. If these crops are infested with budworms then the newer chemistry will be required because pyrethroids would not perform at all.

Chemical choices would be, in alphabetical order: Belt, Steward, or Tracer and possibly Lannate. Some might include Intrepid with this group but I do not know how effective it would be on budworms. Peanut growers should monitor their fields closely for the next 7 to 10 days for budworm numbers. New growers applying a fungicide to soybeans should not automatically add a pyrethroid for insurance purposes. If an insecticide is added in a preventative mode, I would suggest Dimilin at 2 oz. for future foliage feeders.

One other soybean pest that I will mention in closing is soybean loopers. Most soybean fields have a few green cloverworms or an occasional looper. However, one field in Baldwin County was observed last week with about 10 loopers per foot with about 10-15% foliage loss already. Therefore, all fields are not alike and must be scouted to stay on top of the soybean insects.

Soybeans

Loopers are the dominant soybean insect, up to 30% defoliation and damaging levels in some fields. A few velvetbean caterpillar and green cloverworms are in the mix. The “grass” strain of the fall armyworm does not appear to feed to a significant degree on soybeans. And, stink bug populations are not as high as anticipated.

Red banded stink bugs were discovered on the Wiregrass Research Farm, Headland, AL (Henry Co.) this week. Since they were found about 180 miles west of Headland last month, they likely may be present in other locations across south Alabama.

Soybeans

Economic levels of soybean loopers, fall armyworms (FAW) and velvetbean caterpillars (VBC) are as far north as Marion Junction in Dallas county and FAWs are occurring near Prattville in Autauga county. Soybean loopers, usually a southern latitude insect are occurring at all points within the state. Both VBC and FAW can be controlled with less expensive chemistry than can the loopers.

Soybeans

A sub-threshold level of several caterpillar species can be found in most fields statewide. These include green cloverworms, soybean loopers, podworms, fall armyworms, and in the southern areas of the state, velvetbean caterpillars.

If the fall armyworms should occur at treatable levels, growers need to know that they are likely the “grass” strain which can be controlled rather economically with pyrethroids, Intrepid or Dimilin.

Stink bugs, especially the brown species, are at treatable levels in some bean fields. Growers should remember that stink bugs affect the quality of beans more so than the yield. Where brown stink bugs are the primary target, I would suggest a high rate of one of the labeled pyrethroids. These include: Baythroid XL, Brigade (Discipline), Prolex, Karate Z, or Mustang Max. Several of these have multiple generic brand names.