Trials were seeded in 1996 at Western Branch (Tables 9 - 10) and in 1997 at both Western (Table 12) and Northwest Branches (Table 11) to evaluate performance of alfalfa varieties without insecticide treatment to control PLH. The 1996 seeding at Western Branch also evaluates performance of the varieties with preventative insecticide treatment for PLH.
Extremely high PLH populations were present during the summer months at both locations. These trials demonstrate the dramatic improvement in PLH resistance of the glandular-haired varieties. Several of the newest experimental varieties seeded in 1997 show a significant improvement in PLH resistance compared with the first generation varieties which became available commercially in 1997 (Tables 11 - 12). Performance of the experimental glandular-haired varieties has not been compared with that of standard varieties under sprayed conditions in Ohio.
The data from the 1996 seeding at Western Branch (Table 9) shows that insecticide treatment of the glandular-haired varieties is warranted when PLH populations are well over normal economic thresholds, especially in the seeding year. Not treating for PLH in 1996 at Western Branch resulted in lower first harvest yields in 1997. Not treating the remainder of the year also resulted in reduced forage yields for all varieties; however, the yield loss in the glandular-haired varieties was about half of that in the standard susceptible alfalfa varieties (Table 9).
Forage quality of the glandular-haired varieties in the seeding year (1996) at Western Branch compared favorably with that of non-glandular-haired alfalfa (Table 10). Crude protein content and in vitro digestibility were slightly higher for the glandular-haired alfalfa varieties, whether treated with an insecticide or not. Relative feed value differed only slightly among varieties. Forage quality results for 1997 are not yet available. Preliminary studies at University of Wisconsin demonstrated that palatability of hay from a glandular-haired variety was slightly better than hay of Vernal alfalfa. Animal performance trials have not been completed with glandular-haired alfalfa varieties.
The first commercial release of glandular-haired varieties tend to be more dormant than many of the alfalfa varieties grown in Ohio. The glandular-haired varieties broke dormancy later in the spring (see Spring Vigor rating, Table 9), and they tend to regrow slower after harvest. Despite this, forage yield of the glandular-haired varieties was comparable to yield of the standard varieties when treated with an insecticide (Table 9).
These results demonstrate that the new glandular-haired varieties show tremendous promise as a new tool in combating PLH damage in alfalfa. At present, timely insecticide treatment remains the most profitable alternative when PLH pressure is over economic action thresholds; however, PLH resistance of glandular-haired varieties is being improved further. We may soon have varieties that effectively eliminate economic damage by PLH, especially in established stands. The data clearly demonstrates that glandular-haired varieties provide higher forage yields than standard varieties if insecticide control is not applied in a timely manner when PLH populations exceed economic action thresholds.
For more information on potato leafhopper management and control,
see Ohio State University Extension Bulletin 545, Insect Pests of Field
Crops. It is available through county Ohio State University Extension
offices or through Ohioline on the World Wide Web (http://ohioline.ag.ohio-state.edu).
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