Trap Catches to June 25, 2021.
The season is off to a slow start. This is a bit surprising given the warm, dry conditions would be expected to suppress some of the mortality factors that generally limit aphid populations. We have recovered high numbers of non-vector aphid species in the past couple of weeks, but very few PVY vectors are flying.
Most sites have started their trapping and we are getting catch data from an increasing number of sites. We should have most sites up and running by next week.
I anticipate we might start to see cereal aphids dispersing from small grains earlier this year then normal. The grain seems already to be drying and progressing quite rapidly.
We'll keep reporting numbers. As always, keep on scouting!
Scouting for aphids in potatoes:
- Select leaves from the lower to mid canopy. Start at the edge of the field.
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Lower, older leaves will have more established colonies and aphids
prefer the balance of nutrients found here; aphids are rarely found on
leaves in the upper canopy.
- Avoid leaves on the ground or in contact with the soil.
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In seed potatoes there is only a threshold for PLRV (10 aphids/100
leaves), reactive application of insecticides an effective control for
PVY.
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The use of feeding suppressing insecticides, such as pymetrozine
(Fulfill®) or flonicamid (Beleaf®) and refined crop oils, such as Aphoil
and JMS Stylet Oil, at or prior to field colonization by aphids may
reduce the transmission of PVY within fields. Some other insecticides,
such as clothianidin (Belay®), imidacloprid (Admire Pro® or Provado®),
and spirotetramat (Movento®), have also been demonstrated to reduce the
transmission of PVY.
- In table stock potatoes, a treatment threshold of 30 aphids /100 leaves should deter yield loss due to aphid feeding.
The PVY Risk Index Index
Not
all species of aphid are equally efficient at transmitting PVY, some
are better than others (green peach being the most efficient vector of
PVY). So, the total number of aphids in a trap don't necessarily
reflect just how much vector pressure there is at that location. The
PVY Vector Risk Index compares aphid numbers, incorporating their
relative vector efficiency compared to the Queen of PVY vectors (green
peach aphid!). Using averaged reference comparisons from the
literature, we multiply the number of each aphid species captured by its
efficiency compared to Green Peach Aphid to more accurately depict risk
posed by the species being trapped. We then sum the totals. The
PVY-VRI values are presented on the tables below but also on maps
comparing current cumulative risk to the total risk from the sample
sites of last year (to compare with your local winter grow out results).
Click on any image below for full-scale version.