Over the past couple of weeks, first cutting has occurred on alfalfa fields. Make sure second cut regrowth is scouted for potato leafhoppers. The potato leafhopper (PLH) is a major alfalfa insect pest. The PLH does not overwinter in Ohio but is carried northward on storm fronts from the Gulf Coast region each year. We have reports in Ohio that PLH have been found in some alfalfa fields in numbers approaching or exceeding treatment threshold numbers.
The PLH is a sucking insect and feeding by PLH damages the vascular system of the plant and blocks the flow of nutrients. Both adult and nymph (immature adults) stages feed on alfalfa and cause damage. As the number of PLH increases, alfalfa development is stunted resulting in reduced yield. Heavy infestation of PLH will result in the yield reduction of the current cutting as well as subsequent cuttings. A key sign of PLH feeding damage is a wedge-shaped yellowing of leaf tips. By the time this is seen, alfalfa yield has been reduced. Scout fields to detect PLH levels before yield reductions occur.
A sweep net is needed to accurately scout for PLH. Scouting involves taking a 10-pendulum sweep sample from three to five random field locations for every 25 acres of alfalfa. Sampling with a sweep net is best done when the alfalfa is dry. A YouTube video by Mark Sulc, OSU Extension forage specialist, demonstrating how to use a sweep net scouting PLH is available at https://go.osu.edu/scoutingplh. After each 10-sweep sample, count the number of adult and nymph stage PLH. Determine an average plant height in each of the sampled areas.
The economic treatment threshold is dependent upon the average number of PLH collected per 10-sweep sample and the average height of the alfalfa stand. In general, if the average number of PLH in a 10-sweep sample is equal to or exceeds the average height of the alfalfa, then treatment is warranted. For example, if the average alfalfa stand height is 8 inches and sweep net samples average 9 PLH, consider corrective action, such as an insecticide rescue treatment or harvesting early. Harvesting alfalfa temporarily eliminates the nymph stage and disperses the adults. If a foliar insecticide is applied as a rescue option, follow label directions regarding rate and pay attention to the pre-harvest interval. One other PLH management option is the use of PLH resistant alfalfa varieties. These varieties have small, fine hairs on the stems and leaves that deter PLH feeding. The economic treatment threshold for PLH resistant alfalfa is three times a non-PLH resistant variety.
For more information about the PLH life-cycle, management options and treatment threshold levels, consult the OSU Extension fact sheet, “Potato Leafhopper on Alfalfa” available online at https://ohioline.osu.edu/factsheet/ENT-33. For those without internet access, contact the Wayne County Extension office at 330-264-8722 and request a copy of the fact sheet.
Be Careful of Wet Hay and Fire Threat
There has been a lot of hay put up in our area over the past couple of weeks. The challenge in making dry hay is to get enough days of dry weather and sunshine. It is not uncommon when a rain threatens, and the hay is “almost there” to bale it a little on the wet side. In those situations, monitor the hay temperature and note if there is a threat of fire. Every year there are stories and reports of wet hay that ended up starting a shed or barn fire.
Hay will normally undergo some heating in storage. For hay baled at the correct moisture content, normal heating will not exceed 120 degrees F. Hay baled too wet will continue to heat beyond 120 degrees. A worse case scenario is hay baled too wet and then stacked inside a storage structure with limited air movement. In these situations, the temperature can build and reach a point where a fire is started.
If hay has been baled wetter than preferred and put into a storage structure, the temperature should be monitored daily for three to four weeks. Use a thermometer probe that can read temperatures at a six foot or more depth into the stack of bales. At temperatures of 150 F or more the hay is entering a danger zone. If the hay can be moved out of the structure and stacked outside to permit more air movement, this is a good option. Temperatures of 160 F or greater indicate a definite fire danger. Check temperatures every couple of hours and if possible, move hay out of the storage structure and spread bales out to cool them down. If the temperature exceeds 175 F and approaches 190 F or higher, a fire is likely, and the fire department should be notified.