Integrated Pest Management for Apples

JUNE AND JULY (Mid-Summer)

Apple Scab

• Continue to monitor for scab infection periods as described in the dormant and pre-bloom section in order to make timely fungicide applications that stop primary infection.
• Ascospore production and the potential for primary infection is usually completed by early June or once the apples are ½ inch in diameter.
• Make a note of any areas within the orchard where primary infection of foliage is apparent. If you see primary leaf infection, take a closer look at developing fruit to determine the degree of fruit infection.
• Apply sprays to control secondary scab if one or two primary scab lesions per tree are present.

Consider using the Ascospore Maturation Model to help determine when the primary infection period is over.

• Temperature collection equipment in the orchard must be operational by bud break. · This model uses a base temperature of 0 degrees C.
• Calculate daily degree days by averaging the high and low temperature for the day (max plus min/2).
• Keep a running total of accumulated degree days to follow ascospore maturation. Ascospore maturation occurs in three phases:
  1. Lag phase which lasts from 1-149 degree days (about 20% mature during this time).
  2. Accelerated phase which lasts from 149-371 DD (about 70% mature during this time).
  3. Final phase which lasts from 371-427 DD (the final 10% mature).

Note: To use this model either record your temperature in Celsius or convert from Fahrenheit to Celsius. (Degrees Fahrenheit - 32) X 5/9 = Degrees Celsius. Most predictive models or data handling software programs (Onset Computer) allow you to display in either Fahrenheit or Celsius units.

Using the above criteria, the end of the primary scab season occurs after the first daytime rain after 427 DD has been reached. A spray applied at this time should be the last one needed to stop primary infection. This model has not been tested under western Washington conditions. It should be viewed as a tool to help determine the endpoint of ascospore production. If primary infection has not been perfectly controlled, additional fungicide applications may be necessary.

Anthracnose

• June and July is also the time to look for dying 1-year-old shoots caused by girdling cankers, both anthracnose and European.
• Cut these well below the canker and remove from the orchard.

Typical wing-type pheromone trap.

Codling Moth "sting." A recent entry in mature fruit has a small amount of frass surrounded by a red ring.

Codling Moth

Monitoring and decision-making for this pest is based on degree day accumulation and pheromone trap catch results as discussed in the previous section. At this crop stage, pheromone traps should have been in place for several weeks and degree day information is available and being updated at least on a weekly basis. First generation codling moth is usually successfully treated with either one delayed insecticide application timed at 550 total degree days (350 DD after Biofix) or two sprays applied 21 days apart, with the first spray applied at 450 total degree days (250 DD after Biofix). Below is the spray decision making system used successfully by apple growers who cooperated in the Nooksack IPM Project in Whatcom County.

Apply spray if 6 or more moths per trap are caught between 200(BIOFIX) and 450 degree-days (250DD after BIOFIX).

• After this spray, begin recording trap catch again.
• If 6 or more moths are trapped over the next 21 days, apply a second spray.
• If not, then a second spray is not necessary to control first generation.
• If less than 6 moths are trapped from 200(BIOFIX) until 450 degree-days, extend until 550 degree-days (350DD after BIOFIX). If still less than 6 are trapped, do not control. If 6 or more moths are trapped, control at once.

The key decision-making period for first generation codling moth management is during the month of June. Egg hatch for the second generation does not usually begin until late July or early August at a total of about 1250 degree days, or 1000DD after BIOFIX. However, pheromone traps should be maintained during the summer months. As you approach 1200 degree days (1000 DD after BIOFIX), usually in mid to late July, you should:

• Replace pheromone lures and trap bottoms
• Begin recording second generation trap catch on a weekly basis.

As the first generation trap catch begins to drop off in early July, fruit should be examined in the orchard to assess damage from codling moth larvae;

• Examine 100 fruit per site from 4 to 5 sites per block for signs of entry.
• Brown frass (excrement) can be seen on the damaged apple, often surrounded by a reddish ring.
• Cut open the fruit to confirm presence and identification of codling moth larva.
• This is useful in either a low input program or as a tool to evaluate the effectiveness of sprays that have been applied.

White Apple Leafhopper

As mentioned in the previous section, the critical period for monitoring and decision making is mid to late May when the first generation nymphs are hatching and developing. This timing corresponds to approximately 350 degree days (150DD after BIOFIX). Control is usually less effective during June and July when all stages of the insect may be present. First cover sprays for codling moth are usually too late for optimum leafhopper control, but may reduce leafhopper populations somewhat.

BINOMIAL SAMPLING

Spider Mites

pider mites and predatory mites are visible to the naked eye but examination in the field is aided with the use of at least a 10X and more preferably a 15X hand lens. There are essentially two methods for examination of spider mites in the field which can help with decision making.

One method is to collect 25 leaves per site from 4 to 5 sites within a block. Leaves are examined using a hand lens and the total number of spider mites and predatory mites are counted and recorded at each site. Results are tabulated, which provides a picture of the density at various spots in the orchard. This is laborious but it can give a good estimate of spider mite and predatory mite populations. If populations are high, it can be difficult to get an accurate count.. The advantage of this method is that it can provide information on predatory mite and rust mite activity as well, which is useful in decision making.

A second field method is called "Binomial Sampling". In this case, it is not necessary to count the number of mites on each of several leaves, just the number of infested leaves. A leaf is considered infested if it has one or more ERM or two or more TSSM. A typical sampling scheme would be to collect 25 leaves per site and determine the number of infested leaves. This can be repeated at additional sites, collecting up to at least 100 leaves per block. The percentage of leaves infested correlates to the number of mites per leaf, which can be looked up on a chart for the particular species (see page 5-12). This technique gives less precise information and is most useful in low pressure situations. The highest mite density it can measure accurately is 10 mites/leaf, which is well below treatment thresholds (25 to 30 mites/leaf). It also does not allow for in-field assessments of either rust mites or predatory mites, which is important in decision making. The biggest advantage of this sampling method is that it is simple and fast. It should be the first method used in the field in mid to late June to determine quickly whether more intensive sampling needs to be done.

MITE BRUSHING

Mite Brushing Machine.

Mite brushing machine, glass plates, rack and counting grid.

The most precise method is to collect 25 leaves per site in 4 to 5 sites per block and to bag them separately for each site using a labeled, paper bag. Leaves are returned to a lab where they are brushed using a "Mite Brushing Machine" and then counted under a microscope. The brushing machine has opposable rollers covered with soft bristles which brush mites (spider mites, predatory mites, eggs, and rust mites) from the leaf surface and onto a revolving glass plate, which is coated with a very thin, slightly sticky substance (liquid detergent works well). The plate is then transferred to a counting grid, which has 20 wedge-shaped sections. This allows for efficient counting under the microscope. Usually, 10 to 25% of the plate area is counted and then totaled and divided by the number of leaves that were brushed , yielding the number of numerous species of mites per leaf. This method is quite involved but does provide the most accurate population measurements of spider mites and their eggs, predatory mites and their eggs, and apple rust mites. It has been most widely used as a research tool and by independent consultants providing advisory services to growers.

Recommended Spider Mite Sampling Method:

• Start with the binomial sampling method in mid to late June.
• Check populations in 4 to 5 sites per block.
• Record the results after each sample is taken.
• Repeat at approximately 2 week intervals through July and into August.
• Pay particular attention to apple rust mite symptoms in mid July.
• If either apple rust mites or spider mites appear to be approaching treatment threshold, do a more thorough field count or use a mite brushing machine to extract and count mites using a microscope.
• If no predators are detected in successive samples and spider mites or apple rust mites continue to increase, then it may be necessary to apply a miticide.
• Rough treatment thresholds are:
• 30 spider mites per leaf
• 300 apple rust mites per leaf
• A ratio of 1 predatory mite to 10 spider mites usually indicates good potential for biological control to occur.
• Before choosing any pesticide (including fungicide, insecticide, miticide), give consideration to its toxicity to predatory mites if known, and avoid using it if other alternatives are available.
• Mites are more likely to be a problem in the Gala variety and in young orchards, which are less likely to have an established population of predatory mites.