Apple Pest Report: Friday, May 5, 2006
Vol. 14 No. 3
Scab
Now that we've had some rain and warm temperatures, it seems
safe to assume that scab maturation is finally on track. Scab
ascospore maturity and disease risk do not increase in a straight line,
but as an S shaped curve. And the curve is now bending upward with
accelerated maturation and rapidly increasing area of young foliage
tissue for released ascospores to land on.
By the time the next rain arrives, we will be into full blown primary scab season. The showers that started on Tuesday May 2 brought the first significant scab infection period of the year to Highmoor Farm, and accounted for roughly 8% of the season's primary scab infection risk. Lesions from this infection period (if protection was not adequate) will begin showing on leaves as yellowish areas and then as greasy or velvety dark spots around May 17. So until then, it is not worth your time to be checking for scab lesions.
As of Friday night, May 5, there is no rain in the immediate forecast for the Highmoor Farm area. There have been a few quick showers this week that did not keep leaves wet enough to allow scab infection. it would be comforting to think that scab ascospores release in these situations only to die a thirsty death. But scab has been around a long time and is engineered to only release ascospores in conditions the will allow subsequent germination. Looking further ahead in the forecast (dangerous, I know), there is a block of six rainy days in a row from Wednesday to Monday, May 10-15. No doubt that forecast will change in detail as those dates come nearer, but if the long term forecast is generally correct in calling for a long wetting period starting towards the middle of next week, that would bring a scab infection period about four times as potent as this weeks infection period.
Growers would be wise to watch the weather forecast over the coming days and hold off on applying fungicide until as close as possible before the rain starts. Applying too early means your investment in fungicide protection is being depleted by leaf tissue expansion. You don't want to spend money protecting foliage on dry days when no protection is needed. On the other hand, winds can pick up as a new front moves in, so you can't wait until the last dry hour to apply fungicide.
A recent grower spray discussion might be of interest to other folks.
Coverage applied on Saturday April 22 was considered depleted around May
1, then there was the rain starting May 2. Fungicide was reapplied
on Wednesday May 3 right after the infection period. Rubigan with
72-96 hour kickback was used to control any scab infections that
initiated during the weak protection present on the previous day.
The question of the moment was, is a follow-up kickback fungicide
application needed to insure efficacy of the first kickback application?
For what it's worth, my take on it was no. The need for a
7-day-kickback-backup (long name!) is with respect to three criteria.
1) how severe was the infection, and how weak was the
protection?
2) how far past the beginning of infection was the
application made?
3) and (as with any scab discussion) - how much overwintering
scab inoculum is there?
In this case, even though protection from the previous spray
was not reliable there was likely still some protection present.
The infection period was significant, but of relatively slight severity.
And the postinfection application was made with 48 hours of the
beginning of any infections. If any one of these had been
otherwise (high overwintered scab inoculum, major infection period, or
delayed application), then a follow-up application would make sense.
Yes or no does not change the timing of the next fungicide application in this case. That will be early next week as per the expected date for the next rain. But being able to use captan along for that next application will save some money compared to a combined sterol inhibitor + protectant or strobilurin + protectant application.
Insects
and Mites
TARNISHED
PLANT BUG
I'll be checking traps at Highmoor on Monday to inform the Pink spray decision there (and will send out as an email). With the last couple of days of warm sunny weather, I expect to find a few more TPB to increase trap catch from the cumulative average of 0.4 per trap by the end of last week.
Leafminer moths
Leafminer flight has begun, but unless
you are seeing swarms, its more efficient to wait until after petal fall
to gauge the population of sap-feeding mines. Windy weather during
bloom seems to be a deciding factor for how many mines appear. One
good thing about lousy weather during bloom is that keeps a leafminer
population from taking hold.
European Red Mite (ERM)
The warm days this week have advanced the
expected date for the beginning of ERM egg hatch at Highmoor Farm to
Sunday, May 7. The spray window early next week will be the last chance
for high efficacy smothering of overwintering eggs. Orchards with
pink showing should cut the oil rate down to 1% volume-to-volume (i.e. 1
gallon oil in 100 gallons dilute spray mix). You can concentrate
the oil for concentrate spraying, but don't go over 2-3% mix regardless
of how the volume of spray water used compares to the dilute rate for
that size tree (i.e. the concentration factor derived from tree row
volume calculation).
Other arthropods
Dr. Art Agnello of Cornell University wrote the
following for his April 17 Scaffolds Newsletter:
"Rosy Apple Aphid: In particularly susceptible varieties (Cortland, Ida Red, Golden Delicious, R.I. Greening), a material such as Lorsban or Supracide can provide effective prevention through tight cluster, and will pick up any San Jose scale at the same time. Actara is also a good prebloom fit for rosy apple aphid and other pests besides, including leafminers and early plum curculio. You'll also get some side rosy control if you're using Esteem for scale at this time.
San Jose Scale: Besides the Lorsban and Supracide noted above, delayed dormant oil applications will do a good job of reducing scale populations. If you're not treating for rosies but are concerned that SJS might be increasing in some blocks, Esteem is an insect growth regulator with good activity on scale. The label calls for it to be mixed with oil, so if you're applying oil for mites anyway, this might be a tactic to try in severe cases.
Dogwood Borer/American Plum Borer: A coarse spray of Lorsban directed at trunk burr knots between half-inch green and petal fall is the most effective tactic against both species, which can be a problem in dwarf plantings."
Note: the recommended treatment threshold for Rosy apple aphid is 1 or more colonies per 100 fruit clusters, though this is perhaps a bit on the cautious side unless the orchard has a history of problems with this pest.
Even more arthropods
Here are Tight Cluster to Pink thresholds for some
usually minor pests. These species are more likely to be numerous
on low spray trees. Feeding by Green
pug moth, Eastern tent caterpillar, Gypsy moth, and Green fruitworms,
are usually of little importance on established apple trees, but can be
significant on young trees.
Green pug moth, Green fruitworms - 6 larvae
per 100 fruit clusters
Obliquebanded leafroller - 2+ larvae
in first 30 fruit clusters or vegetative terminals, 3+ in 100 (can stop
looking if there are none in first 50)
McIntosh bud stage dates
The following observed and
forecast McIntosh bud stage dates are for Highmoor Farm:
Tight Cluster - May 2
Pink - May 9
King Bloom - May 17 (earlier this year with warm soil temperature?)
Full Bloom - May 19
95% Petal fall - May 26
Fruit Set - June 1
Sincerely,
Glen
Glen Koehler
Pest Management Office
491 College Avenue
Orono, ME 04473
Voice: 207-581-3882
Email:
gkoehler@umext.maine.edu
Web:
PRONewEngland.org
Fax: 207-581-3881
What we call the secret of happiness is no more a secret than our willingness to choose life. - Leo Buscaglia