Jul 25, 2012 - Insect Pest Report #6
By Dr. Vikram Bisht, Plant Pathologist, Potato & Horticultural Crops, Manitoba Agriculture, Foods & Rural Initiatives
Green Peach Aphids have been trapped in 3 of the 9 sites. Other aphid numbers appear to be increasing slightly. All aphids observed were still winged aphids; only one Potato leafhopper (PLH) nymph was noticed on leaf samples collected. Use of mineral oil or insecticide should be considered by seed growers. Insect net sweeps in commercial fields showed higher numbers of leafhoppers (ALH and PLH).
Aster leafhopper (ALH) counts in most crops are very high this year. And with some crops maturing, they will be looking for greener foliage. Normally, the % ALHs infective with aster yellows (AY) is determined to be 2.5%, but early in 2012 the infective ALHs were 12-16% and have dropped to 3 to 6% in the last few weeks (Univ of Wisconsin). Thus a combination of high numbers and higher % of ALHs carrying AY phytoplasma this year has resulted in above normal AY in many crops.
Canola fields are showing a larger number of AY affected plants. In a couple of carrot fields there were >200 ALH/100 insect net sweeps, which is a rather high number as compared to earlier years when the numbers would be around 40-50 at this time of the year. Sweeps in a few commercial potato fields have shown 32 to >100 ALHs/100 sweeps. Yellow sticky card in a field showed >200 ALHs, 31 Potato leaf hopper, 1 aphid and many thrips. Hot weather also seems to be contributing to such high numbers.
Some examples of aster yellows in different crops: potato, carrot, canola, flax, barley, calendula, and petunia. There may be other crops showing AY symptoms.
The number of aphids trapped is given in the table below:
