Pest & Crop Newsletter

Weevils Wreaking Widespread Woes- (John Obermeyer, Rich Edwards, and Larry Bledsoe)

Surveys of west central and northwestern Indiana alfalfa fields this past week (see “Alfalfa Weevil Larval Survey”) reveal that weevil feeding has reached high levels in many fields. Weevil damage and subsequent populations continue to progress faster than anticipated with the given heat unit accumulations. This should be a warning to growers throughout northern Indiana counties.

Many pest managers have or will soon apply insecticides to suppress this feeding frenzy. If possible, insecticides should not be applied until 400 heat units (base 48∞F) have accumulated (see “Weather Update”). At this level, most weevil eggs have hatched and the majority of larvae can be controlled. If treatments are necessary before this time, use products and/or rates that will give long residual control while carefully considering the harvest restrictions. Refer to the recommended insecticides for alfalfa weevil larval control in Pest&Crop #4, April 12, 2002.

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Aphids In Wheat – (John Obermeyer, Rich Edwards, and Larry Bledsoe)

Aphids feeding on developing kernel

A caller this week from southwest Indiana was concerned about the presence of aphids on wheat and disease potential. Barley Yellow Dwarf Virus (BYDV), which is transmitted by aphids, causes yellowing of wheat. BYDV usually is observed in late spring, at about jointing, and usually occurs in patches of varying sizes. Plants infested with aphids in the fall, usually more likely in early plantings, are more likely to be infected with BYDV and severely damaged. Insecticide applications applied after wheat reaches Feekes’ 4.0 does little good to prevent the transmission of BYDV (refer to “Feekes Growth Stages for Wheat” in Pest&Crop, Issue #1).

Watch for aphid population increases as wheat heads begin to emerge and fill. The aphids injure developing heads by sucking plant juices. An average of 50 or more aphids per head indicates that an insecticide treatment should be considered. Normally when aphid numbers build to 10 or more per plant, it is not uncommon for predators and parasites to increase rapidly in response to this increased source of food. Lady beetles (adults and larvae), syrphid fly larvae, lacewing larvae, and several species of parasites are probably now or shortly will be numerous in most fields. These natural control agents should help reduce aphid numbers.

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Showers, Flowers, and Black Cutworm – (John Obermeyer, Rich Edwards, and Larry Bledsoe)

Several intensive captures (9 or more moths caught over 2-nights) have been recorded by our dutiful cooperators throughout the state, see “Black Cutworm Adult Pheromone Trap Report.” This recent flush of moths is attributed to warm wind currents from the Gulf Coast States and southwestern portions of the country.

Significant moth captures at this time, along with the use of heat units to predict the beginning of larval activity, gives us an indication of potential severity of the problem and locations of concern. Thus, we are able to predict with some degree of accuracy when and where crop damage is likely to occur based on these data. Watch for future P&C articles concerning this pest.

Should one treat for black cutworm before or at planting? The tried, true, and economic approach to black cutworm management is to scout fields, determine infestation and damage levels, and use a rescue treatment, if needed. Scouting, treatment thresholds, and control information will be provided in future Pest&Crop newsletters.

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Black Cutworm Adult Pheromone Trap Report

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Armyworm moth

Armyworm Moths Also Arriving – (John Obermeyer, Rich Edwards, and Larry Bledsoe)

Armyworm pheromone traps in Kentucky and one keen observer in Orange County Indiana have confirmed that this dreaded pest from the 2001 season has made its annual arrival into the Midwest. Watch for our black light trap catch reports beginning in next week’s Pest&Crop and subsequent newsletters before jumping to conclusions about this pest in 2002.

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Atrazine and Frogs- (Glenn Nice and Thomas Bauman)

“Ubi dubium ibi libertas” which is Latin for, “Where there is doubt, there is freedom.”  Far too often in the media one study is dictated in such a manner that suggests proof.  The media does this with the full knowledge of what sells.  In fact, as many high school science classes will teach, one study only means that a hypothesis has been supported, never proven.  The word “proof” is almost never heard in research.  We see and hear words like “suggests” and “supports.”  Generally in science, whether it be butterflies or frogs, one study will raise eyebrows that lead to other studies revolving around or repeating the first.  It is important to have a study repeated by others before strong over all conclusions can be made.  An idea or hypothesis has to be supported by others and in the field.

Research recently released by Dr. Tyrone B. Hayes of the University of California at Berkeley suggests that atrazine can interfere with the African clawed frog (Xenopus laevis) sexual development.  Dr. Hayes reported in the Proceedings of the National Academy of Science that atrazine levels from 0.1 ppb to 200 ppb can increase the production of the enzyme aromatase, which is involved in the conversion of androgen hormones to estrogen hormones.  These hormones are involved in the sexual development of the frog.  As the levels of atrazine were increased to 200 ppm up to 20 percent of the frogs showed multiple sex organs.  Vocal chord development was also suggested to be effected.  Which would affect the frogs ability to attract a mate and reproduce.  At present, EPA allows 3 ppb of atrazine in drinking water and the chronic exposure limit for aquatic life is 12 ppb for aquatic life.

Is this a concern for people?  The effects on people have not been addressed by the research.  However, the point is made that unlike frogs people do not live in the water (ABC News.com).  Also unlike frogs, people generally don’t have the ability to change their sex mid life cycle (excluding the use of modern medicine).  In populations of frogs, males can become females if there is an over abundance of male frogs in a population indicating a certain plasticity of sex determination.

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