Upcoming disease and pest problems

Wow, it rained! The watering that many have done over the last year or so has helped keep trees and shrubs alive, but it is not as beneficial as rainwater. Now things are going to start happening with plant development, growth and depending on the humidity and temperatures associated with disease and pest problems. Following are some problems that may show up on a tree near you and how to control them.

Apple scab is a fungal disease to trees and shrubs in the apple family. The disease is most noticeable in mid-summer as dull black or grey-brown lesions on the surface of tree leaves and fruit. The disease rarely kills its host, but can significantly reduce fruit yields and fruit quality. Young leaves are most susceptible to being infected within the first week after unfolding.

Captan can be used to control apple scab on crabapple and apple trees. The first application should be done as the buds swell and open and do two or three more applications spaced 10 days apart. Other fungicides that can be used on ornamental crabapples only are propriconazole contained in such products as Bonide INFUSE Systemic Disease Control, Ferti-Lome Systemic Fungicide Liquid or chlorothalonil contained in such products as Bonide Fungionil, Garden Tech Daconil, Gordon’s Multi-Purpose Fungicide, Ortho Daconil just before the bud sheaths have opened.

Zimmerman Pine Moth is a native insect that has become established throughout northwestern South Dakota. Ponderosa Pines in shelterbelts have been most commonly infested, but Austrian, Mugo, Jack and Scotch Pines are also reported as hosts. It infests the tips of branches and the main trunk feeding on the inner bark. Branches typically break at the crotch area where they join the trunk. Dead and dying branches, most often in the upper half of the tree, commonly indicate infestations. The first external symptoms of injury are popcorn-like pitch masses at wound sites. The pitch masses may reach golf-ball size and ultimately resemble clusters of small, pale grapes. The injury not only retards growth but also deforms the tree. Partially girdled whorls become so weakened that the tree breaks off.

Permethrin contained in products such as Bonide Borer-Mine Killer and Gordon’s Bug-No-More can be used to control this pest. April is normally the time for chemical control but as late of a spring as we are having you should be able to kill the caterpillars in May by soaking the tree and especially the trunk before the temperature warms. When they start crawling about and begin to dig deep into the tree trunk they will be killed by the poison residue on the bark. Repeat the spray application in August to kill young caterpillars that hatch from the eggs.

Diplodia Tip Blight a fungal disease that affects Austrian and Scotch that are growing under stressful conditions. The fungus is known to infect the younger and healthy needles of newly formed candles. It especially attacks the tips and needles of trees that have been weakened by stress from drought, injuries to roots, not enough nutrients in the soil, excessive amounts of shade, as well as injuries inflicted from weather and insects. It shows up as canker like injuries that ooze a resin that serves to infect other trees. The most evident sign of a pine tree being infected is if the trees have brown, stunted new shoots with short, brown needles.

To control treat with a fungicide containing propiconazole or chlorothalanil before the bud sheaths have opened. See above under apple scab for products containing these active ingredients.

Sources: Dr. John Ball, SDDA Forest Health Specialist and USDA Forest Service General Technical Report Diseases of Trees of the Great Plains. If you would like more information about “Upcoming Disease and Pest Problems,” call 605-244-5222, Extension 4.