June 11th AppleTalk Conference Call

AppleTalk Conference Call Summary
Tuesday, June 11, 2019, 8:00 – 9:00 AM
Presenter: John Aue, Threshold IPM
Moderator: Peter Werts, IPM Institute of North America; questions or comments, pwerts@ipminstitute.org

June 11th Call Stream: CLICK HERE

Regional update

Location Degree Days 6/11/2019 (*Base 50°F) Petal Fall Date (NEWA) Accumulated DD* from Petal Fall DD remaining to 308 DD* from Petal Fall CM Biofix (NEWA) Accumulated DD* from CM biofix
Eau Claire, WI 362 6/3/2019 126 182 6/8/2019 40
Gays Mills, WI 458 5/30/2019 194 114 6/6/2019 81
Hastings, MN 426 6/1/2019 167 141 6/7/2019 64
Harvard (Royal Oak), IL 490 5/23/19 260 48 6/7/2019 60
Lake City, MN 437 6/1/2019 165 143 6/3/2019 138
Mauston (Northwoods), WI 417 6/1/2019 150 158 6/7/2019 55
Mequon (Barthel), WI 288 6/6/2019 44 264 No biofix No biofix
Preston, MN 418 5/31/2019 171 137 6/3/2019 127
Rochester (Ela), WI 357 5/31/2019 125 183 5/30/2019 140
Trempealeau (Eckers), WI 423 5/31/2019 173 135 6/6/2019 82
Verona, WI 454 5/30/2019 190 118 6/5/2019 101
White Bear Lake, MN 389 6/3/2019 144 164 6/8/2019 41
Woodstock, IL 505 5/26/2019 264 44 5/28/2019 216

Table 1. Degree day accumulation to 6/11/2019.  Please note: Degree days for plum curculio and codling moth are estimated by NEWA unless entered by users.  This year DD are as much as five days off grower-observed codling moth flights. *All degree days are calculated using a lower-temperature threshold or base temperature of 50°F.

The NEWA insect models for codling moth and plum curculio do not save user data and only display suggested dates for petal fall and codling moth biofix using accumulated degree days.  Growers must enter their own dates for more accurate degree days.  Generally, we are finding these are a bit off this year.  Many areas are showing codling moth (CM) biofixes as June 7th-8th but several growers have reported biofixes anywhere between May 28th and June 9th.  Please send us your biofix dates so we can add them to the degree day table for a more accurate representation of your area.  Growers that have had an earlier biofix are 120-140 degree days (DD) from CM biofix.  According the NEWA dates, locations in the region are showing 60-80 DD from CM biofix.  The same issue is occurring with plum curculio (PC).  Many McIntosh petal fall dates are listed on May 31st and June 1st, with a few on June 6th.  After visiting orchards and discussing with growers, many McIntosh petal fall dates actually occurred between May 23rd-30th.

We are continuing to experience a delayed emergence from both PC and CM due to cooler temperatures.  The cool forecast will continue to result in slow degree day accumulation.  Rather than accumulating 12 to 18 DD base 50°F, most of the region will only be accumulating eight to 12 DD base 50°F.  Rain is expected across the region going into the weekend.

Despite regional differences early in the season and a lag in degree days in some areas, fruit growth has been rapid, and most orchards now have fruit between 12-16mm or larger.  Thinners have been working well, but in some instances, have been working too well despite the cooler temperatures during the four days after thinners were applied.  This includes growers that have used NAA and carbaryl or carbaryl alone at petal fall.  If a thinner was applied within the last week and are planning on applying additional thinners, it is important to measure the size of your king fruit and compare them to the size of side blooms.  If king fruit are 25 to 50% larger than side fruit, then the thinner is being effective and these fruit will likely fall off.  Where fruit are very close in size, additional thinners will be needed.  Avoid using a penetrant such as Regulaid even if fruit are sizing rapidly.

The carbohydrate model suggests that under sunny conditions, trees have very little stress and a surplus of carbohydrates.  Under these conditions the NEWA model might suggest increasing rates of thinners.  However, this is presuming trees are “normal”.  This year we know trees have been under a lot of stress, and this may be why thinners are working very well regardless of the predicted carbohydrate surplus or deficits trees have.

If combination thinners have been applied, e.g., MaxCel (6BA) + Sevin (carbaryl) or Fruitone (NAA) + Sevin (carbaryl), the Michigan Spray Guide recommends not using carbaryl in the second application, as excessive thinning may occur.  Note: The ppm calculations for NAA are not measured as the rate per acre, but rather by the volume of water measured into the tank, e.g., 2, 4 or 6 oz per 100 gallons of water.  It does not matter what the rate per acre of water is, the concentration in ppm will be the same if you thin at 50, 80 or 100 gal./acre.

Nutrient deficiencies
Rapid shoot growth, cool weather and more frequent rain, has induced nutrient deficiencies that are becoming visible on the growing terminals of trees.  If leaves are not looking healthy, a few key notes to make are whether or not the leaves affected are newer or older, e.g., if just the terminals are affected or if the entire tree is affected.  When nutrient problems appear in only the shoots, look at the tip of the shoot vs. the base of the shoot.  If the shoots are affected it is usually indicative of a vascular problem, from a canker disease, rather than a nutrient deficiency.  Nutrient deficiency issues most commonly affect the growing points of the newest leaves.  Depending on the symptoms, an application of 20-20-20 foliar fertilizer at 5 lb./acre is recommended for nutrient deficiencies, even if it is from manganese or zinc as the product also contains micronutrients.  At 5 lb./acre, this will provide 1 lb. of actual nitrogen, phosphorous and potassium, and will help to restore the nutrient balance without over invigorating healthy trees.

A common symptom of micronutrient deficiency, e.g., boron or zinc, includes the yellowing of leaf tissue while leaf veins remain green.  If individual shoots are looking unhealthy, then it is likely a nutrient issue.  If the entire tree is affected and is looking red in color, this could be from oversaturated roots or canker diseases that are compromising the vascular tissue and is not nutrient related.  The most critical time for tree hydration, whether the trees are bearing or non-bearing, is 30 days after bloom.  If the end of June is dryer, well-drained sites may need to monitor for water deficits and shouldn’t wait until July to water.

Resources to help identify nutrient deficiencies and understanding nutrient management:

Phytophthora and water molds
Orchards that continue to hold moisture and remain oversaturated are at risk of invasions from Phytophthora and water molds.  When flooded orchards and soils are saturated for more than a week, the soil biota can become anaerobic.  In addition to supplying a conducive habitat for root-injury-causing soil pathogens like phytophthora, water-logged fields pose a severe risk of tree stress and drowned roots.  Significant death of tree roots can occur after three weeks of over saturation even without standing water on the soil’s surface.  If soils are not drying out, there is little that can be done, and the best option is to apply a phosphorous acid fungicide.

Soils that stay in a clump when squeezed in a fist should be treated with a phosphorous acid fungicide, e.g., Aliette (TH-Agrichemicals), Fosetyl-Al, Phostrol, Rampart (Nutrien), after the soil has dried out a little bit.  The phosphorous acid fungicides are highly systemic, short acting and all function the same way.  They are applied as a foliar spray where they are absorbed into the leaves and are translocated to the roots where the fungicides fight off Phytophthora and soil-based pathogens.  Overuse of these fungicides may result in pathogen resistance.  Make sure to look at the pre-harvest intervals on these fungicides.  Generally, two applications about a month apart are recommended; one application after petal fall and one 30 days later.  It is also important to note that these products are relatively cheap, at $7-8.00 per acre.

Phosphorous acid fungicides should not be tank mixed and need to be applied alone.  These products are formulated to be rapidly absorbed into the leaf tissue, which could pull in other products that are included in the tank mix, and result in phytotoxicity injury.  Leaf burning from captan would be a good example.  The longer the product stays wet on the tree, the more absorption will occur.  Even if the soil dries out, roots may be compromised through the rest of the season.

Where orchards are being established on soils that have a high water-holding capacity or are poorly drained, consider using rootstocks with Phytophthora tolerance, e.g., Geneva rootstocks.  Other rootstocks like M26, M9 should not be planted where Phytophthora has been documented.

Read more about Phytophthora: https://ohioline.osu.edu/factsheet/plpath-fru-06

Insect updates
Codling moth trapping
Trece has not been promoting or using any research on the use of thresholds for the new MESO codling moth mating disruption and stated the reason is due to grower standards varying across the country.  Therefore, we presume there is not much research establishing what threshold should be used.  The threshold for regular mating disruption where there are 200-400 disrupters per acre is one or more in a trap.  The issue with this threshold is that at one trap per five acres without mating disruption or one trap per 2.5 acres with mating disruption, it could still be possible to miss judge the CM population density.  Growers risk missing the first application of a larvicide, if there were no trap catches during the first generation.

With slower DD accumulation, the timeline on applying and reapplying codling moth larvicides will be stretched out.  Typically, when a larvicide is applied at 250 DD from biofix, this will target 3% of the total population.  The percentage of the population being targeted by a larvicide increases to 15% when the spray is delayed to 350 DD.  Peak egg hatch where 50% of the population is hatching occurs around 500 DD and after 650 DD is when egg hatch begins to decline.  Orchards that are not using mating disruption should still target first applications at 250 – 350 DD if trap captures are high, e.g., 10 or more in a week’s time.  Orchards where some traps reach the threshold of five and have other traps that stay below threshold, could delay to 350 DD.

Orchards that are using mating disruption should follow the same approach for determining the need for a larvicide.  If the threshold of five is quickly reached or exceeded, then an application right at 250 or 350 DD would be necessary.  If there is only a slow trickle of one or two moths per week, targeting at peak egg hatch may be a better solution.

Obliquebanded leafroller
Currently, the CM population is low, and many growers are thinking about saving a larvicide application.  Obliquebanded leafrollers are similar to CM in that they are poor fliers and therefore may need extra traps in the orchard.  Most growers only deploy one or two OBLR traps, which may not be enough to accurately capture the population density and pressure.  If the goal is to save an insecticide over the next month, it is important to deploy additional OBLR traps.

Obliquebanded leafroller traps should be hung this week.  Typically, the second generation can cause injury at harvest and larvicides applied during their first generation can significantly reduce summer populations.  If trap counts are high, e.g., in excess of 50 in a week, then larvicides for OBLR may need to be applied.  Note: There is no threshold for OBLR traps, this is just a nominal number based on what we typically observe under high-pressure scenarios.

Plum curculio
Once 308 degree days base 50°F from McIntosh petal fall have been accumulated, this denotes the end of plum curculio (PC) movement from overwintering sites into the orchard.  Plum curculio can continue to cause damage in the orchard after 308 DD have accumulated, if populations are not managed.  Neonicotinoids have good contact efficacy for the first two or three days and then act as an antifeedant or curative agent for another seven to ten days.  It is important to not get complacent due to delayed emergence of PC.

Tree phenology is slightly ahead of insect emergence and development; therefore, we may be well beyond petal fall or first cover and continue to see new invasions of PC.  At a minimum, perimeter applications of insecticides need to be maintained for the next ten days.  If you are making a cover spray for codling moth or lepidopteran species, this may not be adequate for PC and you may need to apply a more effective insecticide along the perimeter.

Insecticide Rainfastness
The frequent rains are not making it easy to determine if our plum curculio or codling moth insecticides will continue to provide efficacy.  As a general rule, one inch of rain removes 50% of the pesticide and two inches of rain removes 100% of the pesticide.  However, the timing of when the rain occurred is also important, e.g., 24 hours or one week.  This link from Michigan State University includes a matrix to help determine when reapplication is necessary: https://www.canr.msu.edu/news/rainfast_characteristics_of_insecticides_on_fruit

What are we not seeing in the orchard this year:
San Jose scale crawlers have not appeared yet and there is still time to deploy monitoring tape.  Dogwood borer adults have not been captured in traps in orchards, however, larvae feeding in bur knots at the base of trunks can still be observed.  Traps deployed in the past week may end up capturing many clearwing moths the size and coloration of wasps.  Dogwood borers are about half the size of these moths and are all black rather than black and yellow striped.

Aphid and mite populations have been very low.  Usually by this time, these pests have appeared in several orchards.  John has observed zero rosy apple or apple grain aphids this spring.  This may indicate that several secondary pests were affected by the polar vortex.

Grower questions:

  1. Can a phosphorous acid fungicide be applied later in the season?
    • Yes, up to 30 days prior to harvest, however, it makes more sense to apply a phosphorous acid fungicide when trees are rapidly growing. John would recommend applying a lower rate unless trees are looking very unhealthy and growers are more concerned.
  1. With the cold, wet spring, can powdery mildew or rust still be an issue?
    • Currently, powdery mildew (PM) and rust is delayed with the only sightings of PM occurring in nurseries. Rain washes off PM spores, making it harder to spread.  It is likely the polar vortex killed most infected buds over the winter.  If PM is present and a fungicide is applied, growers should focus on the health of new growth above the infected portion.  The PM damage at the point where the bud tip was infected will stay that way all season.