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.

Update for the First Week of July

The Alabama cotton crop is growing rapidly resulting from abundant rainfall from multiple thunderstorms that have occurred during the last 10-14 days.

Insect wise things have been rather quiet on cotton but not the case with soybeans which I will discuss later.

Tarnished plant bug numbers have not increased as rapidly as expected in fields that I have observed. An occasional adult and or nymph can be found, depending on the age of the cotton. Migrating adults went to the earlier planted cotton first and have had time to now produce offspring. Cotton planted on April 10 is now blooming in Autauga County, Alabama.

To my surprise, I’m finding as many adult southern green stink bugs as I am adult plant bugs. We need to begin watching stink bugs in early bloom cotton. As I have stated before, these stink bugs will feed on thumb size bolls as soon as the dried bloom sheds. A huge stink bug population is waiting in corn. These adults will migrate to cotton, soybeans and peanuts as corn begins to dry down. This may be the largest population in corn that I have ever observed. There seems to be mating pairs in every corn plant at our research farms in Shorter and Prattville, Alabama this week. Most are the southern green species with an occasional brown in the mix. That will be to our advantage in a few weeks since the pyrethroid chemistry does a nice job controlling the green species.

The other insect that is building on cotton is aphids. They are clumped in terminals on occasional plants in numerous fields at present. These clumps will spread field wide before natural diseases wipe out the population. I would project that aphid population decline will not occur until around July 20.

The most intense insect pressure at present is Kudzu bug populations on soybeans in select fields throughout the state. Ten to 50 adults and over 200 immatures per plant can be found in many April planted beans. More adult Kudzu bugs are moving into beans from Kudzu daily. Beans will have to be scouted weekly for the remainder of this and future seasons. One to three sprays may be needed to protect beans this season. This will open the door to pod and foliage feeding caterpillars for the remainder of the season.

Information on the management and control of the Kudzu bug in soybeans has been posted in blog entries previous to this one and also on the Alabama Crops website (alabamacrops.com).

Kudzu Bug Q&A

by Xing Ping Hu, Extension Entomologist, Auburn University

What is a Kudzu bug?
The Kudzu bug is a small yellowish green lady-beetle-like insect. However, they are not a beetle, but a true stink bug with sucking mouths that sip the juice from plants.

They like to aggregate in clusters and release a very strong, foul odor that you can smell several feet away.

Kudzu bugs are also called lablab bugs, bean bugs, globular stink bugs, and bean plataspids.

Are they a new pest and where did they come from?
Yes, the Kudzu bug is a new pest for us in the United States. Many new people are being introduced to it every day. We will all have to learn the best ways to deal with it.

The Kudzu bug is native to Asia. Genetic markers indicate this bug was likely introduced from Japan.

When did they get here and how widely spread are they now?
It was first reported in Georgia in 2009 and spread to Alabama in October 2010. Since then, it has been spreading like wildfire. By the end of June, it has been confirmed in more than 430 counties across 9 Southern Region States. They are in all but 53 counties in Alabama right now.

How do they spread so rapidly?
Many factors aid in their fast dispersal:

• Hitchhiking on vehicles, airplanes, shipments of products and equipment, and even humans
• They are strong flyers themselves, capable of flying at least a couple of miles
• They are attracted to white and lightly-colored surfaces
• Propensity to migrate
• Diverse and flexible life history and rapid population growth rate
• Availability of primary hosts – kudzu plants and soybean crops
• Most interestingly, the new finding in my lab shows a majority of the adult females become fertilized before overwintering. A single pregnant female can lay egg masses in a new location without the presence of male.

What plants do they infest?
Kudzu bugs are leguminous plant feeders. Their primary host is kudzu plants; that is how they got their name. Of the other leguminous crops, they prefer soybeans to vegetable beans and wisteria vine.

However, they must feed on kudzu or soybeans to be able to reproduce. It is common to see them aggregate and feed on non-legume plants in early spring and late fall when leguminous plants are not available.

If they have been in AL since 2010, why the sudden population outbreak in soybean crops this year?
During the first year of invasion, the population was basically limited to kudzu patches. However, because of the exponential growth, overcrowding populations started to move into soybean fields in 2012 and reached peak outbreak this year.

What is the pest status of kudzu bugs?
They were first considered a nuisance pest in residential areas, but are posing much greater threat than previously thought. In Asian countries, it is a serious pest of soybean and vegetable beans. Here in the United States, besides yield loss of soybeans, it poses threats to international trade of agricultural products to Central America, and is an urban nuisance.

What damages do they cause in soybean crops?
They are slow feeders, sucking plant juice and gradually drawing down a plant’s vigor. They do not eat holes in leaves and do not take bites from pods or seed.

When do kudzu bugs move onto soybean plants and how long they stay in soybean field?
It depends on whether you have early, middle, or later soybean crops and the climate. In 2013, we observed adults of an overwinter generation move to lay egg masses on early-planted soybean crops when they are about 1 ft tall. Nymphs appeared in late May and by the middle of June, nymph population had peaked across the entire soybean field. This was also the optimal time for control treatment.

You will see Kudzu bugs in the field until the soybean plants become unsuitable (not enough juice). Last year’s research showed that Kudzu bug population was greater in early-planted soybeans rather than later-planted soybeans. We are monitoring Kudzu bug population dynamics this year.

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

New Release Information on Kudzu Bug by Tim Reed

STATUS OF THE DISTRIBUTION OF KUDZU BUG IN ALABAMA

The kudzu bug has been “officially” reported to occur in 53 of Alabama’s 67 counties as of June 27. Last year in the first week of June this invasive species had been reported in 15 counties. It is quite likely that this insect is now present in all Alabama counties. Several counties have reported significant populations of kudzu bugs infesting soybeans during June in Alabama in 2013 and numerous fields have been sprayed. 

LIFE CYCLE AND HOSTS OF THE KUDZU BUG

The time required for the kudzu bug to develop from an egg to the adult stage is 6 to 8 weeks. The egg hatches in about 5 days. The kudzu bug has been found on many plants but presently the only host plants on which it is known to reproduce are kudzu, soybean and wisteria.

ECONOMIC THRESHOLDS FOR KUDZU BUG ON SOYBEAN

Thresholds for kudzu bugs infesting soybeans continue to evolve as more information is gained from research efforts. Southeastern entomologists are currently recommending that growers consider using the following thresholds when making kudzu bug treatment decisions: 5 bugs per seedling, until plants are one foot tall. Then, the threshold will change to 10 bugs per plant for plants from 1-2 feet tall. The established threshold of one nymph per sweep  should be used for plants above 2 feet tall. Plants should be sampled at least 50 feet from the edge of the field.

The reason for this is that the adults have an extended migration period (6-8 weeks) and colonize field edges first. If you sample the edges, chances are you will make a spray decision too soon before the migration is over.

WHICH CHEMICALS ARE EFFECTIVE IN CONTROLLING KUDZU BUG IN SOYBEANS

Multiple classes of insecticides have shown activity on kudzu bugs. Insecticide treatments containing bifenthrin, cyhalothrin, zetacypermethrin, carbaryl, or acephate provided greater than 80 percent control 2-5 days after treatment in insecticide efficacy trials conducted in Georgia and South Carolina. Insecticides do not prevent eggs from hatching. Growers actively treating kudzu bugs with broad spectrum insecticides should consider using a preventive application of Dimilin (2 oz/acre rate) at the R2/R3 growth stage for control of velvetbean caterpillars and green cloverworms in July, especially in central and south Alabama which historically have had higher populations of velvetbean caterpillars than north Alabama.

EFFECT OF PLANTING DATE ON KUDZU BUG POPULATIONS IN SOYBEANS

Studies in Georgia and South Carolina have shown that kudzu bug populations are higher on earlier planted soybeans than on later-planted beans.

Tim Reed, Extension Entomologist, Auburn University

Insect and Crop Update for the Week of June 23

After going weeks with light to moderate thrips pressure, damage was heavy on 4-7 leaf cotton in early June, especially in SW Alabama.

Cotton was growing rapidly but thrips damage on true leaves was showing heavy damage from about the 4^th to 7^th true leaf. (Peanuts also were taking heavy damage during this same period.)

The thrips window is over now and we need to shift our focus to spider mites, aphids and the plant bug complex which includes tarnished plant bugs, fleahoppers and an occasional clouded plant bug.

Mites are primarily found in the TN Valley region of North Alabama and some treatments were being applied last week.

I noticed the first aphids on April planted cotton in central Alabama last Friday (June 21).

Plant bug numbers (adults) were down last week but nymphs are beginning to appear in our earliest planted cotton (mid-April). I would suggest using a sweep net to sample adults for the next 2-3 weeks, depending on the age of the cotton. As we approach first bloom I would switch to a drop cloth and concentrate on the presence of immature plant bugs.

Also, field men should now be looking at pinhead square set. Fields surveyed on June 21 were setting about 90% of the fruit. However, some plants had up to 30% square loss at that point. I believe you will find that migrating adult tarnished plant bugs will seek out the earliest planted and most lush cotton fields. My thought is that this cotton provides the best shade from the 95 degree temperatures, and is the best host for plant bugs.

While looking for pinhead square set I noticed a number of white eggs, likely tobacco budworms. They would not be a concern now, but in the old days it would have created a real predicament. Spraying for plant bugs during a budworm moth flight would have been expensive and also put the grower on a treatment treadmill for the remainder of the season. Sometimes we forget how well we have it compared to the pre-Bollgard years.

On another insect – a few stink bugs are already present in cotton. Normally we do not worry about stink bugs until about the third week of bloom, when we have bolls that are 10-12 days old. However, when stink bugs are present at bloom they will attack thumb sized bolls as soon as the bloom tag sheds. Any feeding to bolls this size will cause the boll to abort. Therefore, fieldmen need to be alert for adult stink bugs in early bloom cotton as they monitor for plant bugs with a sweepnet. Stink bugs will not damage squares or blooms but will seek out these first small bolls.

Since some of our corn was planted later than desired, stink bugs will likely remain with that host until the post roasting ear stage when the kernels become hard. At that time we may have a large movement into other crops such as cotton, soybeans and peanuts.

One word about Kudzu bugs on soybeans. Numbers of adults are out of site on many of our April planted beans. In fact, adult numbers are beginning to decrease in some fields now but numerous immatures are present, which is the trigger we use to treat the field. Fieldmen who have not experienced this insect may overlook these immatures when they are small. They will be a clear to greenish color and very small after hatching.

Kudzu Bugs Infesting Soybeans

Kudzu bugs (adults and immatures) infesting April planted soybeans on Auburn University research farm, Auburn, AL.

Immatures

 

Immatures

Adults

Adults