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August 1st Pest Alert Message


August 1, 2023

Heat stress is being seen on many plants and humans now! Things like leaf rolling and cupping, wilting, dry leaf edges, blossom and leaf drop, bolting of vegetables, sunscald and blossom end rot. Deep watering, mulching and providing shade will help alleviate these symptoms.

Black rotten looking spots on the bottom of your tomatoes is called blossom end rot. It is caused by a watering imbalance which inhibits the plants ability to take up calcium. A calcium supplement like rot stop will help reduce the problem. It is mostly seen with container grown tomatoes.

There are few serious insect pests at this point in the summer. The one exception is poplar borer. We are seeing Poplar borer egg-laying activity (fresh sawdust) on Aspen tree trunks now. If you find sawdust on your Aspen trunks, now is the time to apply an insecticide trunk spray. The pesticide options are synthetic pyrethroids such as cyfluthrin or permethrin.

We are still spraying for the codling moth as often as your pesticide of choice indicates.

The 2nd generation of apple skelatonizers are active on trees now, but unless you have a significant amount there would be no need to spray. They only affect the foliage   Bt (Bacillus thuringensis) is the spray to use.

The only way to protect your apples from bird damage is to cover the tree with netting. 

The brown tips you are seeing on Larch, Douglas Fir and Spruce trees is due to the spruce budworm or tussock moth. There is no need to spray now, most of these insects do their feeding in the late spring/early summer as new growth develops.

Fall webworm caterpillars are forming silken webs in apple, cherry and chokecherry trees now. Cut out limb or spray with Bt (bacillus thuringensis) to control them.

Powdery mildew is being seen on perennials, apple & maple trees now, try to keep water off leaves, or water mid morning to give the foliage time to dry. Most cases are not severe enough to spray a fungicide.

Cedar-apple rust is causing yellow to orange spots on hawthorn trees now. It is to late to spray, instead spray sulfur next spring when leaves emerge.

Aphid populations are decreasing in our sample sites. In most cases there is no need to spray for these pests this late in the season. Mark woody shrubs and trees that have aphids now and remember to treat them with a dormant oil spray next spring. Spider mite populations are still high in most locations. Insecticidal soap plus 1 tbsp of sulfur per gallon and spray the undersides of leaves thoroughly. Be careful on applying sulfur in this heat, early morning or late evening applications.

Some plum, ornamental plum, and cherry tree leaves have lacy holes from pear slug feeding. But unless populations are high (more than 50% of leaves infested), there is no need to treat this pest now.

Grasshoppers are  still around in some locations. If they are a serious problem, you can apply carbaryl-treated bran baits to affected plants. These insecticide-laced baits can injure birds if they eat them

Keep on deep soaking trees and shrubs every 7-10 days. Fruit trees need a lot of water to fully develop a nice crop.

Come check out our booth at the fair August 9th and 10th – join the Rocky Mountain Garden membership drive - cultivating your connection to community and the natural world. And maybe you will win the red flyer wagon filled with all kinds of plants, canning & gardening supplies.