February 2018

This cold snap makes it feel like winter has finally decided to show, but scouting for pests has revealed that pear psylla are already on the move and laying! With that in mind, now is a good time to review the dormant/ delayed dormant oil sprays that are typically the first line of defense at the beginning of the season. The dormant season is a critical period for various pest management activities:

Several key insect and mite pests overwinter in orchards and are vulnerable to sprays.
Because leaves are off the tree, good spray coverage is easier to obtain.
Beneficial insects and mites are less affected by sprays during dormancy.
Several pests are concentrated on the twigs and shoots, making dormant season an excellent time for monitoring and assessing their populations.

Dormancy is generally defined as the period from leaf fall until growth resumes in spring. Delayed dormancy is the period from the resumption of growth, indicated by bud swell until green tip.

Dormant versus delayed-dormant treatments. If the main target is San Jose scale, then a dormant timing (before bud swell) for treatment is usually best. It should be noted that San Jose scale has been found in some orchards this past season, so this spray will be critical for early control!! Control of peach silver mite and peach twig borer larvae in hibernacula is effective at either timing. European red mites (eggs), two spotted spider mites and obliquebanded leafroller larvae are best controlled using delayed-dormant timing.

Following is a list of key blight/ pests targeted with dormant/ delayed dormant sprays based on our location here on the Western Slope. A description of each is provided to aid in understanding its biology.

Coryneum Blight

The main symptoms of shot hole on peach occur on twigs and buds, but fruit lesions may develop when spring weather is wet. Twig symptoms first appear as small, purplish black spots. These turn brown as they enlarge, often having a light center with a purplish brown margin. Tiny, dark brown bumps develop at the center of each lesion.

Fruit and leaf symptoms look much like those of twig lesions. They are small spots, purplish at first, and turning light brown in the center as they enlarge. Sporodochia form in leaf lesions but not in fruit lesions. Leaf lesions may be surrounded by a light green or yellowish zone; in many cases the brown tissue in the center will fall out, leaving the "shot hole" that gives the disease its name.

Wilsonomyces carpophilus survives on infected twigs and buds. Spores are produced throughout winter and are spread by splashing rain and wind. The disease is favored by prolonged wetness in fall to mid-winter (twig blight). Summer rain or sprinkler irrigation encourages fruit infection. There is more infection low in the tree where fruit stay wet longer.

**NOTICE**

At the recent WCHS conference, a statement was made by Kevin Day referring to the use of copper and its effect on bark hardening, or causing peach bark to become brittle. I’ve had several growers ask about this topic, so I have contacted Kevin in regard to his statements made during the session. After several emails back and forth, here’s the feedback Kevin provided for clarification:

“Please note that I never said not to use copper; in fact, I asked several times what pathogens were of concern without any answer. That is why I did not say not to use copper.

I did however say that annual copper treatments result in trees with rougher bark than trees treated with other products.

I'm not being evasive, but I don't have enough information to make declarative statements about best product use for your area. I do know that bark texture, color and general health are affected by fungicide choice, and that is why I suggested someone look into evaluating alternatives.

I hope this is of some value. Please let me know.”

I have not been able to locate any research data indicating copper having a negative effect on tree bark. Also, we don’t know the types of copper or product rates used in reference to his statement. Please keep that in mind and don’t throw out the baby with the bath water on this one!

Pear Psylla

Pear psylla is the first pest we scout for. It is one of the most serious insect pest of pears because of its ability to develop resistance to insecticides and to vector the pathogen that causes pear decline.

Tiny, elongated yellowish eggs, which are barely visible without a hand lens, are laid on or near fruit spurs starting early in the season as temperatures start to warm up. As buds open, females lay eggs along midribs and petioles of developing leaves or on stems and leaves of blossoms.

Pear psylla damages pears in several ways. Loss of crop and tree vigor, and sometimes loss of trees, can occur from pear decline disease, caused by a phytoplasma organism that psylla injects into pear trees.

Honeydew, produced by psylla nymphs as they feed, drops onto fruit. A black sooty mold grows on the honeydew and the fruit skin russets, which downgrades fruit for fresh-market use. Psylla feeding and injection of a toxin into the tree causes portions of the leaf blade to blacken, and leaves to yellow and sometimes fall. Growth and productivity of the tree can be severely reduced for one or more seasons.

Green Apple Aphids

Overwintering eggs are found on twigs of the previous season's growth and on fruit spurs. They are identical in appearance to rosy apple aphid eggs: shiny, black, and football shaped. Newly hatched apple aphids are dark green. Mature aphids on apple foliage in spring and summer have a bright, yellow-green abdomen with darker green lateral spots.

Green apple aphid feeds on both apple and pear; apple, however, is the preferred host. Although green apple aphid is subject to wide fluctuations in abundance, it generally occurs yearly in most apple orchards. Natural enemies often control this aphid.

Rosy Apple Aphids

Newly hatched rosy apple aphids are dark green and are found on new growth in early spring. Mature rosy apple aphids, clustering in curled leaves or on young fruits in spring, are purplish and covered with a waxy, powdery bloom. In fall, winged forms develop and migrate back to the apple trees. Overwintering eggs are laid on fruit spurs and shoots of the apple trees; they are shiny, black, and elongated.

This is potentially the most damaging aphid species on apples. Rosy apple aphids cluster on leaves of fruit spurs and growing shoots where they cause severe leaf curling. Fruits on heavily infested fruit spurs fail to properly develop and become misshapen.

Green Peach Aphid

The green peach aphid overwinters as an egg stage on the bark of fruit trees, specifically peach, cherry, apricot and plum. Egg hatch occurs about the time of peach bloom. The green peach aphid has both a sexual and asexual form. The majority of reproduction occurs asexually by a process called pathogenesis where live young are produced. Development occurs very quickly, growing from neonate to adult in as few as 5 days. After 3 or 4 generations on fruit trees, winged adults develop which disperse to other hosts including many vegetable crops.

Green peach aphid is generally pale green, although at times individuals may be present that are pinkish. During cool weather, individuals are usually more deeply pigmented. Both winged and wingless forms of the green peach aphid have prominent cornicles on the abdomen that are markedly swollen and clublike in appearance. The frontal tubercles at the base of the antennae are very prominent and are convergent. Winged forms of the green peach aphid have a distinct dark patch near the tip of the abdomen; wingless forms lack this dark patch.

San Jose Scale

Female San Jose scales give birth to living young that emerge from under the edge of the scale covering. These tiny yellow crawlers wander in a random fashion until they find a suitable place to settle. Immediately upon settling, the crawlers insert their mouthparts into the host plant and begin feeding and secreting a white waxy material (white cap stage); eventually the waxy covering turns black and is known as the black cap stage. Later the covers turn various shades from gray to black.

San Jose scales overwinter predominantly in the black cap stage, although in mild years some adult mated females may also survive. Early in the season, these nymphs resume their growth. Immature male and female scales are indistinguishable until the first molt.

If heavy scale infestations are left unchecked, trees may be seriously damaged, resulting in reduced vigor, thin foliage, cracked or dying branches, and the eventual death of the tree. Young trees may be killed before fruiting. Infested fruit develop a reddish purple ring surrounding each spot where a scale settles.

European Red Mite

European red mites overwinter as eggs; eggs hatch in spring when trees bloom. With the use of a hand lens, look for overwintering eggs in roughened bark at bases of buds and spurs on smaller branches and twigs, or in wounds. They are globular and red with a slender stalk (stipe) rising from the top center and many grooves extending from top to bottom. During the growing season, eggs are laid on leaves. There are three instars before the adult stage. Immature mites are bright red, except just after molting when they appear bright green. The green color turns to red after the mites resume feeding. Adults are dark red and have six to eight white spots at the base of hairs on the back.

Pearleaf Blister Mite

Pearleaf blister mites feed under the bud scales during winter and may cause buds to dry and fail to develop in spring. When buds start to grow in spring, mites feed on emerging leaves from green tip through bloom and also on developing fruit. Feeding on fruit results in oval russet spots, usually depressed with a surrounding halo of clear tissue. These spots are 0.25 to 0.50 inch in diameter and frequently run together. When damaged fruit matures, it is often deformed and misshaped. Leaf feeding causes small blisters which are first red and later turn black (looks like small volcanos). Leaf function can be seriously impaired. Eggs are laid in the blisters and young mites feed inside the blister, thus they are rarely seen.

Two-spotted Spider Mite

Two-spotted spider mites overwinter as adult females in protected places on the tree or in the litter, trash, and weeds on the orchard floor. The overwintering forms are reddish orange. The mites become active in early spring soon after trees leaf out and begin feeding on weeds or in the lower part of the trees.

Stone fruits can tolerate some mite damage, particularly on water sprouts in the center of trees. Two-spotted mites generally feed on the lower leaf surface. Feeding causes a mottling of the leaves, and under severe conditions, can cause heavy leaf drop. They produce heavy webbing. If defoliation happens early in the season, fruit fails to size properly, and limbs and fruit may be exposed to sunburn.

Peach Twig Borer (PTB)

Peach twig borer overwinters on the tree as a first- or second-instar larva within a tiny cell, called a hibernaculum, that is located in crotches of 1- to 3-year-old wood, in pruning wounds, or in deep cracks in bark. The overwintering site is marked by a chimney of frass and is especially noticeable when first constructed or before winter rains set in. Larvae emerge in early spring, usually just before and during bloom, and migrate up twigs and branches where they attack newly emerged leaves, blossoms, and shoots. As shoots elongate, larvae mine the inside, causing the terminals to die back. Dead shoots are known as shoot strikes or flags.

Peach twig borer can be controlled with a spray in the delayed dormant season to kill overwintering larvae in the hibernacula. Dormant sprays of oil alone or oil combined with an insecticide, however, have the advantage of controlling some other stone fruit pests, especially mites, aphids and San Jose scale. (Oil alone does not control peach twig borer.) Mating disruption for PTB during the growing season can also be used to supplement dormant sprays.

Side Notes

Drones- as technology continues to progress, the agriculture industry moves along with it and utilizes the benefits of what it has to offer. Drones are becoming quite popular, especially among large acre farms, as they cover a lot of ground and provide a birds eye view of what’s going on in the orchard. You may have noticed a booth at the recent WCHS trade show displaying a drone used for ag purposes. Some of the services drone scouting can provide are;

- Full service crop scouting

- Crop health analysis

- Stand count

- Yield analysis w/ monetary translation

- Nitrogen soil analysis

- Crop damage reports

- Drainage and irrigation analysis

- Easy to read reports

If you’re interested in drone crop scouting, here’s a link to a local guy: https://www.aeroscout.io . Ben Skogan lives in GJ and is the owner and operator.

Throughout the season, the Cropworx crew works hard to keep your needs met with timely deliveries and also removal of empty oil barrels and shuttles. These barrels/ shuttles go through a rigorous cleaning process and are then put right back into rotation with more material. They are costly to replace and each year more barrels/ shuttles seem to disappear. The cost of these units are not passed along to the customer, and we need your help in getting them back after they’re empty. Please help us in our efforts to save the barrels/ shuttles and let them have long, illustrious life cycles meeting your needs with the chemicals we provide. If you have empty barrels/ totes please let us know!

Credits

Much of this helpful information has been extrapolated from a number of websites, research documents and other literature we have reviewed over the winter lull. Please feel free to contact us so we can design a program with your needs in mind! Cropworx is ready to start the season with you, as we have a full inventory of spray materials and the expertise to meet your needs. Here’s to a successful season!!!