April 29th, AppleTalk Call Summary

AppleTalk Conference Call Summary
Tuesday, April 29th, 2014, 8:00 – 9:00 a.m.
Presenter: John Aue, Threshold IPM.
Moderator: Peter Werts, IPM Institute of North America; questions or comments, pwerts@ipminstitute.org

April 29th Call download: Click here

Tree phenology
Tree phenology from northern Illinois to central Wisconsin varies from half-inch green on early varieties, e.g., Zestar, in northern Illinois to silver tip near Lake Winnebago.  One grower near Madison reports tight cluster on Zestar.

Tree health: cold wet weather and the lasting effects of 2012 heat and drought
Tree stress from the 2012 drought could still increase susceptibility to black rot, white rot, winter injury and decreased blossom production.  These issues are less likely to be a concern, if trees were irrigated in 2012.

Drought impacts
The impacts of heat and drought experienced by many growers in 2012 will continue to have an effect on tree health especially with our below normal temperatures and cloudy, wet weather.  Trees which are still at silver tip are at less of a risk with our current conditions than ones who are already on their way to half-inch green. As the presence of green tissue increases the trees energy demand also increases and with the cold, cloudy weather we are forecasted to have for the next 14 days these trees may struggle to create sugars through photosynthesis.  If you are worried about tree health John recommends to starting thinking about a pre bloom foliar feeding program for these trees.  In order for foliar sprays to be effective there must be leaf tissue to absorb the applied nutrients.  Phil Schwallier of Michigan State University is a potential guest speaker on this topic.

Impacts of cold winter and spring on disease
Winter injury to young shoots may occur when temperatures of negative 5°F are reached.  These same temperatures of 5⁰F below zero and colder may cause powdery mildew infected shoots and inoculum to die and can reduce the amount of spores that cause infections in the spring.  Note: Captan and EBDC’s are not effective on powdery mildew.

Rusts
Rust diseases include cedar apple rust and hawthorn rust is not likely to have been impacted by cold temperatures in Minnesota and Wisconsin this winter.

Scab
Late season snow cover and colder temperatures will result in scab maturing later than previous years. Early sprays might be critical on blocks with high inoculum.  If legions were present on leaves last fall, a scab spray may be necessary at green tip.  Note: scab models start at McIntosh green tip and use a lower developmental threshold starting at 32⁰F.

Impacts of cold winter and spring on insects
A good rule of thumb to follow is insects which overwinter as adults or eggs are usually not affected by cold temperatures.  The following are a few comments on overwintering survivorship of several important pests of apples in the upper Midwest.

Apple maggot
Apple maggot pupae are protected from cold winter temperatures and snow by overwintering in the soil.

Plum curculio
Plum curculio overwinter as an adult weevil and stay protected under the top few inches of soil and leaf litter and are not impacted by cold winter temperatures.  It is questionable whether the short term warm temperatures were enough to drive them above ground.  If this did occur the subsequent cold temperatures would have killed them off.  The cool spring temperatures are not favorable for plum curculio.  They may be out after last week but are certainly not moving into orchards.  If they emerge now, this may reduce their numbers in orchards as petal fall may arrive after the adult’s energy reserves are depleted.

Codling moth
Codling moth overwinter as a full grown larva on trees and temperatures below -15⁰F will provide some mortality.  Sustained cold temperature may have reduced populations in some regions.

European red mite
European red mite eggs can be found around the base of buds and fruit spurs.  John has seen many clear eggs this spring in orchards in southwestern Wisconsin and may suggest they died from low temperatures.

Green apple and rosy apple aphid
Overwintering eggs are not impacted by cold temperatures, however populations may be impacted if they hatch and it is too cold for them to feed.  In 2012 bud break happened on March 17th and half-inch green by March 18th, and aphids were present the very first day.  This year it is likely we will see green apple aphid beyond green tip.  Note: this is not the same for wooly apple aphids which overwinter underground.

Green fruitworm
Green fruitworm overwinter as an adult and is not affected by cold.  John has already noticed them flying in southern Wisconsin orchards.  Monitoring green fruitworm larvae should be done as we enter into bloom.

Obliquebanded leafroller
Overwinter as a second or third instar larva on the tree and could be impacted at anytime from cold temps over the winter.  A cooler spring will allow longer period of predation by migratory birds.

Copper application timing and rates
Whether it be Champ, Kocide, Bordeau or C-O-C-S, the effectiveness is dependent on the amount of copper ion in the formula rather than the formulation.  Consult the Michigan State University (MSU) spray guide and the equivalent amount of copper ion in the formulation.  The MSU spray guide indicates dry/ liquid amounts per unit of material so you can tell the amount of the ion being applied.

Consider that 1.5 to 2.0 lb of actual copper metal per acre has shown to have impacts on blossom blight.  If 4lbs of product, such as C-O-C-S is applied and the label states it is 50% copper you will only be applying 2lb of actual copper.  With the late spring, 6lb of actual copper could be problematic as per risk of russeting.  Early applications of copper run the risk of being washed off by rain before bloom.  If growers decide to apply copper later, after the wet weather passes, it will have a shorter time to weather off.  John is anticipating the buds will develop quickly from bud break to petal fall and if too much copper is present during bloom it runs the risk of causing fruit russeting.

Due to the cold weather, Patty McManus, University of Wisconsin, has concerns on the effectiveness of copper for fireblight control this year.  Bacteria are not growing right now and require warmer temperatures.  The benefit of having already applied copper is that will provide seven days of scab protection at green tip.  If there is a break in the weather and you want to apply a fungicide consider spraying EBDC, e.g., Polyram (metiram) or Penncozeb, Dithane and Koverall (mancozeb).

Scab management and when to tank mix
Managing apple scab early in the season can be very challenging, below is the Modified Mills Chart which outlines temperature and wetting-period parameters for apple scab infections.  The following can be considered when making early season decisions on scab sprays:

  • If your orchard is not at green tip, weather is not an issue.
  • If your weather station has indicated an infection, but there is no green tissue, then there is no risk of a scab infection.  If you are at green tip and beyond, you probably have had a scab infection.
  • If there is green tissue and you have had an infection consider the level of scab management at end of last year.  High inoculum levels will result in an abundance of secondary conidia or ascospore that will increase changes of infection.  Conidia that overwinter in bud scales can impact green tissue and secondary scab spores lodged in the buds pose significant risk.  A light dew can result in growth of conidia and infections that will be impossible to eradicate.
  • After an infection it is not possible to eradicate apple scab.

Modified Mills Chart

Temp. (F)

Hours of Leaf Wetness Required

Light
(Risk of Infection)

Medium
(Risk of Infection)

Severe
(Risk of Infection)

32 to 41

37

48

73

43

26

34

51

44

21

27

40

46

18

23

34

48

15

20

30

50

14

19

28

52

12

17

26

54

11

16

24

55

10

15

22

57

10

14

21

59

9

13

20

61

9

12

19

63

9

12

18

64

9

12

18

66

9

12

18

68

9

12

18

70

9

12

18

72

9

12

18

73

9

12

18

75

9

12

19

77

10

14

21

Table 1. Modified Mills Table. Credit: Gemplers

When to tank mix other products with a protectant fungicide
Anilopyrimadine fungicides, e.g., Vangard (cyprodinil) and Scala (pyrimethanil) work well in cool weather and should be tank mixed with a protectant.  Since there is little green tissue, the spray should be concentrated as much as possible, if spraying Scala or Vanguard in the next 10-14 days.

Keep in mind, sterol inhibitors, Rally (myclobutanil) or Indar (fenbuconazole) and strobilurins like Flint (trifloxystrobin) or Sovran (kresoxim-methyl) do not work as well in cold weather.  More importantly there is not enough leaf tissue present to absorb enough material.  The same rule applies for SDHI fungicides, e.g., Luna Sensation (fluopyram, trifloxystrobin), Fontelis (penthiopyrad) and Merivon (fluxapyroxad, pyraclostrobin).  These products are better to use when scab pressure is highest and the weather is warm.

Delayed dormant oil timing San Jose scale and mite management
Anecdotally, growers are having more success with managing aphids, mites and scale by spreading an oil application over two or three sprays from ½ green to pink at 1-2% concentration.  This increases the chances that one of the applications is going on when it is warm enough for the insect to be at the correct growth stage.  San Jose scale over winter as a crawler on the tree and are protected by a waxy coating.  The overwintering scale will begin to feed as soon as sap begins to flow.  The early spray is the most important and the longer SJS has to feed, the stronger they become and are harder to control.

Where growers are experiencing severe SJS infestations, an application of oil with a growth regulator, such as Esteem (pyriproxyfen), may be applied at half-inch green.

Mites can be targeted with later oil sprays closer to pink. When scouting for mites and SJS check for eggs on 2nd year wood.

http://msue.anr.msu.edu/news/look_for_san_jose_scale_while_pruning_sweet_cherries

Additional online resources:

Michigan State University Fruit Production Digest provides regional updates on crop development, insect, weed and disease management, and more.  http://visitor.r20.constantcontact.com/manage/optin/ea?v=001hQ_goXPHame8y22DTJhyQA%3D%3D

Scaffolds Fruit Journal is a weekly publication by Cornell University that discusses pertinent IPM topics and horticulture tips from March-September.  http://www.scaffolds.entomology.cornell.edu/

Utah State University Tree Fruit IPM Pest Advisories high resolution photos accompany weekly IPM updates for the state of Utah.  http://utahpests.usu.edu/IPM/htm/advisories/treefruit/