Weekly Pest Alerts for May 2018

Douglas County Extension Horticulture, Weekly Pest Alert Comments - 2018 by Steve Renquist
Questions? Email steve.renquist@oregonstate.edu or call 541-236-3047

May 28

The SWD catches in the cherry orchards continue to be very large with counts over 50 again. Anyone with cherry crops that are starting to color need to make their first control spray this week if they did not spray last week. If you sprayed a week ago and your cherry crop is not ripening quickly because of the cool weather this week, you may need to make another spray next week.

Codling moth traps had 3-4 moths in them this week at locations where no spray was made last week. No codling moth catches were made this week in orchards that were sprayed last week. The most critical spray for codling moth control is often the first one that usually falls in late May for the Umpqua Valley. This spray will work to keep a lid on the overall codling moth population as the summer progresses. It is also important to keep monitoring your traps all summer into September and when you catch two moths in one week, make another spray. Remember to clean out your traps each time you record the weekly catch numbers. Always rotate your chemical sprays after each application to minimize resistance buildup.

I noticed pretty heavy pressure from flea beetles on new seedlings in my vegetable garden again this year following the mowing and shredding of the cover crop. Cover crops are great for the soil but during the decomposition phase in the new garden, the insects that aid organic matter decomposition can start chewing on new seedlings. If you have problems with new seedlings being eaten, one application of Spinosad will usually be all that is needed to give them time to grow past the pests.

If you have grapevines that are not hybrids or concords with powdery mildew resistance, it is a good time to make your first fungicide spray. There are a number of fungicides that work well for homeowners but the easiest to find is sulfur. Sulfur is also good for homeowners since you can use it several times in a row without worrying about resistance developing.   

Previous May Weekly Pest Alerts

May 21

The cherry crop has started to color with the warmer weather. This has made a big jump in the
SWD catches in the vinegar traps this week. Several of traps had catches with over 50 with
both male and female SWD present. It looks like a good time to make a control spray if you
have any cherries beginning to color. Spinosad or Malathion are chemical choices for
homeowners to control SWD. Don’t wait too long to spray with potential pressure this high.
Codling moth traps also had 2-3 moths this week. That is enough to hit the spray threshold so
now is a good time to make that spray too. Spinosad, Cyd-X, and Surround, are organic
options, while Malathion and Sevin will work for conventional controls. If your traps had one
or no catches, you can wait another week and monitor. Your fruit thinning for apple, pear, peach, and plum should be finished by the end of May to ensure a good bloom and fruit set for next year. Don’t wait too long.

May 14

I found no new codling moth in my traps this week so I did not have to make a spray. The
vinegard traps for Spotted Wing Drosophila were also not catching much. It is still pretty
early for any of the fruit crops to be attracting SWD. As the cherry, and berry crops ripen the
SWD will come in fast with big numbers. I did notice some apple scab on leaves of apples and
on ornamental crab apple. One more protective spray should be made if we get rain forecast
within the next week.

May 7

A mild winter pushed all the fruit trees to bloom about 2-3 weeks earlier than the last couple
of years. The mild winter was followed by a cool spring slowing crop progress a little for both
berry crops and tree fruit. With average to slightly above average heat unit accumulation year
to date, insect emergence has been right on the twenty year averages. One of my codling
moth traps did pick up 4 moths over the past week and a second trap caught 6 moths. These
catches are at or over the needed threshold of 5, so clean out the traps and make your first
codling moth sprays for apples, pears, and plums within the next 10 days. As we go forward
always remember to clean out the traps so your new weekly monitoring will be accurate. As
we move into the new week any trap with 2 or more moth catches should be followed with
another spray. For organic growers when we start our codling moth spray program use
Spinosad, Cyd-X, Surround, horticultural oil, or superior oil. If you are not an organic grower
you can use non organic products like sevin or malathion. Don’t use the oil products on your
fruit trees if the temperature is over 85 degrees at any time during the day or within two days
following the spray. This year has had a couple hot days in early May so make sure none are
forecast when you use any oil based products.

We are also monitoring for apple or pear scab presently. I noticed on several Gala apple trees
new scab infection on leaves. It is important to put fungicides on your fruit trees, grapevines
and berry crops to protect them from powdery mildew, scab, or other fungal diseases. You
should always put on a fungicide spray to prevent these diseases so get the spray on now if the
weather forecast looks dry for a day or two. Organic growers are restricted to using dusting
sulfur or wettable sulfur. Conventional growers can use captan, or immunox. Buy 2 or more
insecticide products, and alternate their use as I advise the timing in the weeks ahead to
prevent resistance by insects. Sulfur is a product that has not experienced disease resistance
issues.

Remember to get vinegar traps out in your orchard and berry crops to monitor for Spotted
Wing Drosophila. These small vinegar flies have been laying eggs in berry, cherry, and peach
crops the past few seasons and will need to be controlled as your fruit crop gets near full size.
I will advise you when to apply controls, however it is important to know if they are around
your fruit crops presently.

Researchers have been trapping Brown Marmorated Stink Bugs (BMSB) around much of
western Oregon during the past year. These insects can cause a major amount of damage to
fruit and vegetable crops so look up what they look like and keep alert. These pests especially
like English holly and Tree of Heaven (Ailanthus altissima) to gather and live in. Researchers
have been getting good control of these pests by treating the ornamental host plants with systemic insecticides. I have put out some traps in several areas of Garden Valley to follow
the population buildup of the BMSB.

With the slightly early tree fruit growing season you should plan to start fruit thinning about
20-30 days after petal fall. We saw petal fall from most tree fruit crops in mid to late April.
Apples, pears, peaches, and plums often set way to much fruit. Thinning fruit will improve
size and quality, plus keep your tree branches from breaking. When you are thinning off fruit
look for damaged fruit and remove them. Pears, peaches, and plums bloomed early this year
so thinning should commence now. Wait on apples until May 12.