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POTATO LEAFHOPPERS IN ALFALFA

Potato leafhoppers have the potential to hurt alfalfa in Nebraska every year. This is generally a second and third cutting pest and has been common in Nebraska recently. Southerly winds bring this insect into Nebraska , as is does not overwinter here. There have been a lot of strong southerly winds the last couple of weeks, so it is probable we have potato leafhoppers in the state. So, it is time to begin scouting.

These small (1/8 inch long), bright green, wedge shaped insects (Fig 1) may cause severe damage to alfalfa by injecting a toxin into the plant as they feed. This feeding results in a distinctive yellow or purple triangle shape at the tip of the leaf. First year spring planted alfalfa fields are particularly attractive to and vulnerable to potato leafhoppers, as are fields planted last year. In older fields, these insects are usually a problem on second and third cuttings. Newly developed resistant varieties will protect from potato leafhoppers fairly well, but alfalfa in the seedling stage may still be damaged. All fields should still be scouted, as large numbers of leafhoppers may still cause a problem, even in resistant variety fields.

Fig. 1. Adult potato leafhopper

Treatment decisions are based on numbers captured by sweep net. A sweep net is the only reliable way to scout for potato leafhoppers. See the following tables for decision-making help. Note that there do not have to be many to cause a problem. A large number of insecticides are registered for control, and all will provide good results when applied properly. Commonly used insecticides include Mustang, Warrior, Baythroid, and Lorsban. If possible, refer to the UNL Department of Entomology Web site at http://entomology.unl.edu/instabls/alfpotleaf.htm for a list of suggested insecticides. (KJ)

Table 1. Dynamic Treatment Thresholds for Potato Leafhoppers (average number per sweep) on Alfalfa that is 1 to 4 inches tall.

Table 2. Dynamic Treatment Thresholds for Potato Leafhoppers (average number per sweep) on Alfalfa that is 4 to 8 inches tall.

Table 3. Dynamic Treatment Thresholds for Potato Leafhoppers (average number per sweep) on Alfalfa that is 8 to 12 inches tall.

FLAMING: POTENTIAL NEW TOOL FOR WEED CONTROL IN ORGANICALLY GROWN AGRONOMIC CROPS

Purpose of this article is to provide some general facts about organic crop production, and a brief update on the flaming study, which is the newest addition to the weed science program for Northeast NE.

There is an increased interest in organic production among farmers and industries with the current organic food sales totaling $15 billion (2.5% of the food market). Demand for organics is expected to continue, with the estimated sales of organic foods of $25 billion by 2010.

Growth in organic food sales has brought additional farmland into organic production, totaling about 4 million acres nationwide. Nebraska was ranked 9th nationally in 2006 in certified organic crops acres (80,000) and 10 th in certified organic pasture acres (20,000). Of all agronomic crops, the most common ones are wheat (20,000 acres), corn (15,000 acres), soybeans (10,000 acres) and alfalfa (10,000 acres).

Organic producers rank weeds as their number one problem. Hand weeding and cultivation are the most popular physical methods for weed control utilized by organic growers. However, hand weeding is becoming cost prohibitive, while repeated cultivation increases the chance for soil erosion and promotes emergence of new weed flushes. In addition, there are only several organic herbicides approved for use in organic production, and they are very expensive (can cost over a $1000/acre). Therefore, there is a need to evaluate various alternative and integrated methods of weed control. The use of propane for flame weeding could be one of the alternative control methods for weed control in organically grown agronomic crops.

During flaming process, the heat from the flame is transferred to the plant tissues increasing the thermal energy of the plant cells and resulting in coagulation of cell proteins if the temperature is above 50C. Furthermore, exposing plant tissue to a temperature of about 100C for a split second (eg. 0.1 second) can result in cell membrane rupture, resulting in loss of water and plant death.

In order to optimize use of flame, as a weed control tool, we are currently conducting a series of experiments to obtain baseline information on crop and weed tolerance to broadcast flaming in Nebraska . As part of a graduate student thesis (Santiago Ulloa, PhD student) the dose response curves of propane will be described for control of 12 major weed species and tolerance of 6 major agronomic crops. We believe that depending on the desired level of weed control, or tolerable crop injury level, a propane dose could be selected to either control the weed, or reduce its growth thereby offsetting its competitive ability against the crop.

Flaming in our project is conducted using a custom built flamer mounted on an ATV, which produced open flames utilizing propane as source of combustion. There are four burners (LT 2x8) placed 30 cm apart.

Based on the first year of data, broadleaf weeds and broadleaf crops were more susceptible to flaming than grassy species. About 80% control was achieved with a propane rate of 4 gallons per acre (GPA) for velvetleaf and pigweed, compared to 8GPA for barnyardgrass and 7GPA in green foxtail. There was no complete kill of barnyardgrass and green foxtail as the plants re-grew in 3-4 weeks. Despite the regrowth, flaming provided early season control of both grassy species by severely reducing their growth, and thereby offsetting their competitive ability against the crop. Similarly, corn and sorghum were less susceptible to flaming than soybean and sunflower. The difference is likely a result of the physical positioning of the species' growing point at the time of flaming. The growing point in broadleaf species was above the ground, thus exposed to the flame. In contrary, the growing point in grassy species during early growth stages was below the soil surface, thus protected from the flame.

From a practical standpoint, flaming has a potential to be utilized as a very effective tool for managing broadleaf weeds and suppressing an early season growth of grasses. Of all crops tested, broadcast flaming has the most potential for use in field corn. These studies are continuing into the 2008 and 2009 seasons, thus feel free to contact Dr. Stevan Knezevic for additional information at 402-584-2808, or e-mail KNEZEVIC2@UNL.EDU ).

David P. Shelton
Extension Agricultural Engineer

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