July 18, AppleTalk Conference Call

AppleTalk Conference Call Summary
Tuesday, July 18 2017, 8:00 – 8:45 AM
Presenter: John Aue, Threshold IPM
Moderator: Peter Werts, IPM Institute of North America; questions or comments, pwerts@ipminstitute.org

July 18th Call Stream: CLICK HERE

Plant nutrient analysis
In mid-July thru early August (approximately 60 days after petal fall) is when we can collect soil and foliar samples to complete a nutrient analysis to help guide nutrient-management decisions. As a general rule, apple trees should be on a maintenance program where nutrients are applied based on soil and tissue results from the previous season. Trees should be second leaf or older before collecting tissue samples. Fully developed leaves need to be selected from the middle of this year’s growing shoots. Only collect one leaf per tree and a total of 20 – 30 leaves per sampling area, to generate about a cup of dried plant material for the analysis. Avoid mixing healthy trees with a block or group of trees showing deficiencies, as trees showing signs of poor vigor or nutrient deficiencies should be collected in separate samples.

The UW Soils and Forage Lab offers a plant analysis as one packaged service that $25 per sample and includes both soil and foliar results. Additional soil tests for calcium + magnesium, boron, zinc, manganese, and sulfur (SO4-S) are available for $3 each. Apple trees don’t readily take up boron, sulfur and zinc through the root system, so there is not much utility in these additional soil tests. The tissue test will give results for total nitrogen and total minerals, which include: phosphorous, potassium, calcium, magnesium, sulfur, zinc, boron, manganese, iron and copper. Collect a representative soil sample from within the area the leaves were gathered. The sample should represent a 2-10” soil depth and use care to discard the top 1-2” of soil profile from sample core or location. Minimize the inclusion of roots and other debris.

UW Soil and Forage Lab, https://uwlab.soils.wisc.edu/plant-tissue/
• Plant analysis submission form, Front: https://uwlab.triforce.cals.wisc.edu/wp-content/uploads/sites/343/sites/17/2011/06/pa_front_SFAL-1.pdf
• Plant analysis submission form, Back: https://uwlab.triforce.cals.wisc.edu/wp-content/uploads/sites/343/sites/17/2016/02/pa_back_sfal.pdf

Nutrition Guidelines for Tree Fruits in Wisconsin
Silver leaf disease
We have been observing a significant amount of silver leaf, a rather obscure disease. There has been little research done on this disease and no known fungicides that act on the pathogen. It has been commented by some plant pathologists that the symptoms of silver leaf will occasionally disappear. The current recommendations are to prune out infections. However, silver leaf infections occur in the plant tissue below the part of the tree which show the visual symptoms, therefore, pruning out branches with silver leaf may not eradicate the actual pathogen. Pictures and additional descriptions of the symptoms are available here, http://msue.anr.msu.edu/news/silver_leaf_of_tree_fruits.

Codling moth
We are now past our 1000 degree-day mark from the start of first generation codling moth biofix. Most of the time trap counts drop off and we can see a distinct gap in the flights. However, for some growers with high pressure, the flights never drop off to zero. This is when we need to use our degree days to make a decision on when a flight is now part of the second generation and to switch insecticide modes of action.

Unlike in the spring, insecticides targeting second generation codling moth should not be delayed past 250 degree days (DD), base 50°F, from biofix. We are able to delay in the spring, because adverse weather conditions and rain during the first flight often reduce the fecundity of female codling moths. In late summer, we have excellent weather for codling moth mating and can expect a strong flight to require treatment at 250 DD, base 50°F.

The treatment threshold is five moths per trap and after a biofix has been established, blocks that do not go over threshold may not require treatment. This could be helpful as we near harvest and allow for spot treatments only of blocks which caught five moths or more in a weeks’ time.

Sequential sampling of mite populations offer a quick and easy way to assess mite populations. The sampling method uses a presence or absence count which correlates to an assumed average number of mites per leaf across the entire block being sampled. When we can sample frequently, this is often the quickest method to identify if a block needs to be treated with a miticide. This sampling method does not account for the days mites have been on the leaves or if any predators are present. For example, mites can be below threshold, but still causing bronzing, which means we have economic damage. Additionally, we can deduct a positive count for mites for each leaf where we see a mite predator, so a leaf with a mite and a mite predator would be marked as being absent of mites. Prolonged feeding can stress the tree by impacting photosynthesis and can lead to reduced shoot growth and fruit bud set the following year and in severe cause impact winter hardiness.

Summer oils are the primary insecticide option for organic growers and should be applied during a cool and cloudy day. Introducing natural predators could be successful option for some growers: Biological Control of European Red Mite in Northeast Apples: An Implementation Guide for Growers, https://ecommons.cornell.edu/bitstream/handle/1813/43090/erm-biocontrol-FS-NYSIPM.pdf?sequence=1.

If you are going to apply a miticide as rescue treatment (populations are over threshold or bronzing is occurring) look for a miticide that controls all motile forms, as there are miticides which only affect eggs or adults. All miticides should be rotated between applications and seasons. Please note, miticide rates may vary between two-spotted spider mites vs. European red mites and not all miticides will control apple rust mites. Apple rust mites do not have thresholds and are generally not a concern on large semi-dwarf trees, but may be of concern for trees that are newly planted or on trellised systems. Populations of 200-500 per leaf are often needed to cause injury, and may justify treatment.

Sequential mite sampling July 1-31: http://newa.cornell.edu/uploads/mites50.pdf

Sequential mite sampling July 1-15: http://newa.cornell.edu/uploads/mites75.pdf

Miticide options which preserve predator mites
Envidor (spirodiclofen) Insecticide Resistance Action Committee (IRAC) 23
Portal (fenpyroximate) IRAC 21A
Nealta (cyflumetofen) IRAC 25
Zeal SC (etoxazole) IRAC 10B
Acramite 50 WS (bifenazate) IRAC UN
Kanemite 15 SC (acequinocyl) IRAC 20B

Choices: Mite Management Tools & Biological Control, The Jentsch Lab, July 6 2016, http://blogs.cornell.edu/jentsch/2016/07/06/choices-mite-management-tools-biological-control/

Bitter pit
Adapted from August 11 2015, AppleTalk Conference Call with guest speaker Dr. Amaya Atucha, University of Wisconsin- Madison

Calcium (Ca) is important for fruit quality and the majority of Ca is taken into the fruit during the cell expansion phase from petal fall to the end of July (~50 days after petal fall). After this period, the xylem in the fruit losses efficiency especially in the calyx end. Calcium does not easily move from the soil to the fruit and is relatively immobile within the tree. Concentrations can vary between foliage, fruit and soil. Note: Foliar Ca levels will be greater than what is in fruit since high transpiration rate in the leaves cause more Ca to accumulate. The following factors can influence Ca levels and incidence of bitter pit: Nutrient imbalances with nitrogen (N), potassium (K) and boron (B), soil moisture levels and fruit size.

Keys to reducing bitter pit
1) Submit foliar, fruit and soil samples for nutrient and pH analysis. It is recommended to test samples for all available macro/micro nutrients as many complex interactions exist. For example: an excess amount of magnesium (Mg) or potassium (K) will compete with Ca for uptake.
2) Keep soils adequately hydrated throughout entire growing season.
3) Reduce excessive vegetative growth; Apogee (prohexadione calcium) can be applied to curb vegetative growth. Reducing vegetative growth will redirect the transport of Ca from foliage to fruit. The pre-harvest interval for Apogee is 45 days.
4) Lite crops or excessive thinning can result in large fruit. Calcium levels can be diluted in large fruit; Ca concentrations typically vary from stem to calyx end (location where bitter pit symptoms are most pronounced), excessively large fruit usually have exacerbated symptoms.
5) Calcium sprays can begin at petal fall and continue to end of August; up to six applications may be necessary. Coverage is important, Ca most contact fruit to be effective. The recommended rate is 1-2 lb. Ca per 100 gallons of water. If visible symptoms are present it is not too late to apply Ca to prevent further injury.