WHEAT
Fungicidal Control of Fusarium Head Blight (Head Scab) and Deoxynivalenol (DON) in Wheat By Don Hershman
Background Information.  Fusarium head blight (FHB) of wheat, and deoxynivalenol (DON) accumulation in harvested grain, are periodically very serious problems in Kentucky. There was minimal FHB or DON in 2006-2008 in Kentucky, but each year brings new possibilities. Thus, it is imperative that you be on guard for FHB/DON in 2009. Since this time last year, several new fungicides have received Section 3 labels from EPA and can now be used to suppress both FHB and DON.  Caramba (BASF), Prosaro and Proline (Bayer), and several tebuconazole products (e.g., Folicur, Bayer) can now be legally applied at early crop anthesis (flowering) for disease suppression. Previously, various propiconazole products (e.g., Tilt – Syngenta) were labeled for FHB control. The Regional Wheat Disease Committee, NCERA 208, has reviewed existing efficacy data and has concluded that Caramba, Prosaro and Proline provide “good” control of FHB and DON.  Tebuconazole fungicides were given a “fair” rating, and propiconazole products were given a “poor” rating. Note: none of the products provide excellent control of either FHB or DON.  Thus, it is still possible to take a serious yield and quality hit if FHB pressure is high this season. Fungicides are certainly not the silver bullet for FHB management. In fact, they do work best when applied to wheat varieties that have at least some resistance to FHB. Excellent fungicide coverage on wheat heads is crucial to achieve the greatest possible FHB/DON suppression.  This is no small challenge since most spray systems used in wheat were developed to deliver pesticides to foliage (horizontal structures).  In order to maximize coverage on heads (vertical targets), significant changes may need to be made to the sprayer boom system. Also, discipline must be exercised to ensure that proper sprayer pressure and volumes are used. Be sure to precisely follow all fungicide label instructions and restrictions. Making Appropriate Fungicide Spray Decisions.  One desire we all have is for fungicides to be used only when needed.  Regular field scouting for foliar fungal diseases has been successfully used by growers for many years to determine if and when to spray fungicides in wheat. However, this is not possible with FHB since once symptoms are present it is TOO LATE to spray.  Below are some general guidelines to help you determine if you should spray fungicides for FHB/DON suppression. During period leading up to, during and immediately after head emergence: Soil moisture has been good for the past month (relates to spore production, dispersal of Fusarium graminearum spores, and crop infection). Crop has good yield potential (relates to economics and crop density, which increases canopy humidity and may increase spore production, facilitate spore dispersal, and encourage crop infection). Temperatures 68-86 F (relates to spore production and crop infection). Humidity is high (80% day or night) and/or free water (such as dew) is present on the heads during this period (relates to spore production, dispersal, and crop infection). If most or all of the above conditions exist when the crop is just beginning to flower, consider spraying as soon as possible.                    New Web-Based FHB Prediction Tool.  In addition to the above general guidelines, an exciting new tool can also be used to help determine the FHB risk and need to spray.  This tool is a web-based, disease forecasting model made available by Penn State University, The Ohio State University, Kansas State University, and the U.S. Wheat and Barley Scab Initiative.  This forecasting model, utilizes real-time weather data from numerous National Weather Service stations within each state.   Go to www.wheatscab.psu.edu/ and click on “Risk map tool”.    You will be asked if you are growing winter or spring wheat.  At this point you will come to a U.S. map and are asked to click on the state of interest.  The FHB Risk Management Tool page will have a map that shows where the weather data are being retrieved.  To the upper left corner of the page is a calendar section labeled “Assessment Date”. This section needs a bit of explaining. You will note right away that the tool will only let you click on the current date and the preceding 7 days.  So, if you estimate your crop will begin to flower (the beginning of FHB susceptibility) on May 7, but it is only May 3, the best you will be able to do is to determine if the weather on May 3 (or the previous 7 days) is favorable for FHB. My advice is to begin determining the FHB risk using this model 1-2 weeks out from crop flowering. Keep checking your wheat and keep checking the model every 1-2 days.  By the time your crop reaches early flowering, you should have a good feel for the FHB risk in your area.  If the forecast model says the FHB risk is high (medium if you are not a risk taker), and the forecast matches your local weather and crop reality, then you might consider spraying as soon as possible.  The FHB Risk Management Tool also includes a commentary section that will give you a text risk assessment based on the opinion of the local state Extension Specialist (that’s me for KY).  Once you actually see it and play around with it, what I have said above will make much more sense.  The model does have several practical limitations in predicting final FHB levels; these are clearly discussed within the Prediction Center website.  Perhaps the greatest limitation of the model is that it does not account for weather conditions during flowering and grain fill. Specifically, disease-favorable weather occurring during late flowering and grain fill can greatly impact final FHB/DON levels. The bottom line is that final FHB/DON levels may not always be reflected by the model’s risk output.  The authors of the model discuss this limitation under “Reality Check” in the “Model Details” section of the Prediction Center.   We all hope that FHB is non-existent this spring.  However, if this is not the case, wheat producers now have an additional tool to use to minimize FHB and DON development this spring.
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FRUIT CROPS
Estimating Risks of Fire Blight Infection By John Hartman
Fire blight of apple and pear, caused by the bacterium, Erwinia amylovora, kills blossoms, fruit spurs, shoots, limbs and, sometimes, whole trees.  Fire blight disease in Kentucky is difficult to control.  It is unpredictable; epidemics can strike quickly in young orchards where it has never been a problem and yet, in some years, mature orchards with a long history of fire blight may show little disease.  Fire blight control is also difficult because the best available antibiotic, streptomycin, works well only when used just before blossom infections occur.  An important concept in fire blight management is that infection of the flowers provides a large quantity of inoculum for continued spread of fire blight in the shoots and branches. Preventing fire blight infections during bloom with timely applications of the antibiotic should be the goal.  Can fire blight be predicted?  To relate fire blight infection biology to weather conditions, disease models have been developed.  Maryblyt (developed by Dr. Paul Steiner, University of Maryland and Gary Lightner, USDA/AFRS, Kearnysville, WV) and Cougarblight (developed by Dr. Timothy Smith, Washington State University) are computer-assisted disease models for predicting fire blight.  These models use measurements of temperature and wetness in the orchard to predict infection of open apple or pear flowers by E. amylovora. Both models pre-suppose that fire blight primary infection is a four step process: Erwinia amylovora bacteria, emerging around last year’s fire blight cankers, must be moved to the open flowers by rain-splash or by foraging bees. The bacteria must grow and develop a colony on the flower large enough to cause an infection. Gentle rain or other wetness is needed to wash the bacteria to the base of the flowers and into the open nectaries so E. amylovora can get into the plant. Once inside the flower, suitable temperatures will allow the bacteria to continue growing as a parasite and to move within the blossom spur and eventually the tree’s twigs and branches. To predict whether or not a threat from fire blight exists one must know how much bacterial growth might occur on the stigmas of apple and pear flowers.  This growth is temperature dependent, so prediction of infection risk requires knowing the temperature while flowers are open (Figures 1, 2, & 3) using degree hour data or average daily temperatures and relating it to rate of bacterial growth at similar temperatures in the laboratory.  These calculations, based on recorded temperatures, are done by the computer or they can be done using specially prepared charts.  Temperatures determine both the number of days the flower may be infected and degree of bacterial colony growth. Wetness is the potential trigger of infection, as water moves the bacteria into the nectaries.  Typically, while flowers are open, 2-4 days of warm weather, followed by a rain or heavy dew provides conditions needed for infection.  Using the disease models, risk potential in the near future may be evaluated with forecasted temperatures.  Thus, managing primary infections of the tree via the flowers can be aided substantially through the use of Maryblyt or Cougarblight.  By knowing daily high and low temperatures, rainfall, and tree development stage the computer or the grower calculates when fire blight infections have occurred or when they are likely to occur.  When blossom blight occurs, early symptoms often show ooze droplets or browning of blossom pedicels.  The infection of a single flower in a cluster usually kills the entire spur (Figure 4).  As the disease progresses bacteria invade the supporting twig, causing a canker that girdles it, resulting in the loss of other nearby spurs.  From the bacteria that build up from these primary infections, infection of new, elongating shoots occurs.  The resulting shoot blight, or twig blight, is the most visible and damaging phase of fire blight (Figure 5).  Early shoot blight symptoms show a slight wilt of the shoot tip, sometimes with ooze droplets visible on the stem.  This is soon followed by leaf and shoot browning and death which proceeds down the shoot.  Will disease predictive systems work?  During the past week, apples have been in bloom throughout Kentucky.  Warm weather occurred on Friday and Saturday, April 17&18.  Then rain moved in on Sunday and Monday.  Was it warm enough for long enough for fire blight to pose a significant threat?  Using the Cougarblight model on Mesonet and National Weather Service data from 44 Kentucky locations indicates that in 27 of the locations, fire blight infection risk was high or fairly high and growers would have wanted to apply streptomycin.  However, in the other 17 locations, fire blight infection risk was low or marginal and sprays may not have been needed.  Some Kentucky growers have used the disease models to determine whether or not to spray.  Several years ago, the Maryblyt system was used to calculate the need for fire blight applications by participating Kentucky apple growers.  In years with low disease pressure, growers saved one or more streptomycin sprays, with no decrease in tree health, by following these recommendations.  Figure legends: Figure 1.  Apple blossom at the pink stage, not susceptible to fire blight infection. Figure 2.  Apple blossom open and susceptible to infection. Figure 3.  Apple blossom at petal-fall stage and no longer susceptible to infection. Figure 4.  Apple blossom/fruit spur killed by fire blight. Figure 5.  Apple orchard with numerous dead shoots killed by fire blight.
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HOUSEHOLD INSECTS

Rice Weevils - Common Stored Seed Insect By Lee Townsend

Several specimens of the rice weevil, a common pest of stored whole grains and seeds, have been sent in for identification during the past 3 weeks.  Usually, infestations are discovered when these 1/8-inch long dark beetles with distinct snouts are found.  The adult is a wanderer but the legless, grub-like larvae feed and develop inside grain kernels.  Following about a one month life cycle, adults leave through small round exit holes in the grain and repeat the cycle. Rice weevils live for several months and can wander far from their development site.  They can be found throughout the year but are most commonly seen during the winter or early spring.  They are a nuisance but do not bite or sting.  However, they can find and infest other seeds and grains. The key to eliminating rice weevils is to find and destroy the infested products that are their breeding sites. These are most likely to be whole wheat, oats, rye, buckwheat, barley, corn, or rice; even seeds in beanbag chairs can be infested.  Forgotten bags of bird seed and dried arrangements with seeds (especially decorative corn) also can be sources of the weevils.  Breeding sites must be found and eliminated to end the infestation. Spraying to kill adults will not solve the problem.  All life stages can be killed by extreme heat (120°F for one hour) or cold (0°F for a week).  This may be a practical way to end infestations where the stored commodity must be kept.  Otherwise, infested materials should be discarded.  Vacuuming the area with a crevice tool can help to capture hiding weevils.

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NOTE: Trade names are used to simplify the information presented in this newsletter. No endorsement by the Cooperative Extension Service is intended, nor is criticism implied of similar products that are not named.

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