Powdery Mildew

Last week I mentioned powdery mildew which was on point since quite a few people brought in and sent pictures of this fungus. Let’s go into a little more depth about this topic. The fungus gets into the leaf tissue and sends up fruiting structures which look like talcum powder on the leaves. This disease is plant specific meaning that the powdery mildew on the lilacs does not infect garden vegetables. Powdery mildew on phlox will not spread to other flowers.

Powdery Mildew on lilacs

If you find this talcum-like fungus on trees and shrubs do not worry this late in the season. It will not harm these woody plants except for ever-blooming roses. If it is on cucumbers and they are still in their prime bearing mode or winter and summer squash, I recommend treating these plants.

Powdery Mildew on a squash leaf

Use a garden fungicide like Daconil or a sulfur-based fungicide if you can find it to protect the leaves that are not infected. Sulfur is good because it is volatile and will get underneath the leaves. Some horticultural oils and even a 10% milk solution help coat the leaves protecting them from infection. Even washing the leaves helps reduce the spore amount. For roses and flowers, I would use a garden fungicide this late in the season to protect the unaffected leaves.

Some squash leaves have a natural variation of mottled light green of their leaves. This is natural and not a disease.

Powdery Mildew on a rose bush

Powdery mildew has not been a problem for the last couple of years because it was hotter and dryer. This year is different with the rainfall and cooler night temperatures which is the perfect conditions for spreading the disease.

This Week in the Garden (August 6th)

Powdery mildew fungus on a squash leaf.

This week in the garden, let’s start with powdery mildew that is starting to affect certain plants like squash vines. It looks like talcum powder sprinkled on the leaves. This fungus can attack most plants, especially lilacs, but rarely does any damage and shrubs or trees. I do use a fungicide like Daconil on my vining vegetable this time of year with another application after any rains to prevent infestations on summer and winter squash.

Blister beetles.

People in the country have noticed black or dark grey beetles eating certain flowers and vegetables. These are blister beetles usually coming from grazing land or alfalfa fields after being cut. They get their name from a secretion that will cause blisters if crushed or handled. Rarely do they cause much damage.

Tomato hornworm on a tomato plant.

The insect that will cause damage is the tomato hornworm. You may go out to your tomatoes and find a lot of the leaves that have been eaten. Look closely and you will find a green caterpillar the size of your pinky finger. It is easiest to pick them off the plant. These caterpillars will pupate into the large sphinx moth you see fluttering around now on the flowers.

Hedge balls in a bushel basket in a grocery store.

I have seen hedge balls being sold the last time in Pierre. They are the large non-edible fruit from the Osage orange tree. The wood was made into bows and baseball bats. The tree has been used around orchards as a trained hedge to eat critters away. Now the oil in the seeds is used in cosmetics. People use them for spider control in homes claiming they repel spiders and cockroaches away. SDSU rather busted this myth. While some oils in the fruit can act as a repellant, they had to extract and concentrate those oils to have any benefit. Using a border insecticide long-lasting spray around the home like Home Defense Spray will do much more in repelling insects.

Aster yellows affecting a white coneflower..

Aster yellows have been showing up in my asters this year. The first time I tried annual asters and ended up with only 50% of a crop. This is a bacteria spread by mainly leaf hoppers. This bacterium can also infect calendula, petunia, zinnia, mum, cosmos, marigold, coneflower, and other flowers. The symptoms are a stunted plant with brown edges on the leaves and odd-looking flowers. The only remedy is to remove the plant immediately to prevent the infection from going to other plants.

Keep deadheading (flower removal) of your flowerbed and containers. This keeps the flowers producing through the heat of summer into fall. I am deadheading calendulas and Mexican sunflowers every other day, fortunately, I planted just of few of these plants. Zinnia, cosmos, and marigold need weekly deadheading.

This is the time to prepare your soil to plant a lawn into. Spray the area with Roundup to kill everything. Rototill and smooth the ground and plant the grass seed. For shady areas buy a grass mix with fine fescue seed.

This Week in the Garden (Aug. 2nd)

Picture of a Japanese Beetle on a leaf

This week in the garden, it seems a new pest is coming to our area. This is the Japanese beetle which will lay eggs on grass. The eggs hatch and feed on grass roots then hatch into adults. Like grasshoppers, they will eat most crops, especially corn. Fortunately, they have only been found in the eastern part of South Dakota. Their numbers have remained low. You may see the traps around monitoring any activity.

Western Cicada on a tree branch

You may have heard the buzzing mating call of the cicadas in trees last week. The old adage is 6 weeks till frost, hopefully not true. The cicada life cycle in our state varies from 2-5 years, not the 17-year cicada back in the eastern USA. This insect rarely does any damage to the trees.

Wilted tomato plant due to overwatering

I got a few questions about plants in containers wilting and dying, however, they get watered every day. Plants wilt and die from no water or too much water especially if there is no drainage hole in the pot. Constantly wet soil reduces oxygen in the soil killing the root of the plants and causing wilting. Let the top few inches of the soil dry out before watering.

Field cricket

Now to the invasion of crickets. I am finding a lot of crickets around the house. In the flower beds and garden, crickets are usually not a problem. But in the home, I am looking under the stove and refrigerator spraying Raid beneath everything to kill the insect. After a few hours, I found it was on top of the refrigerator, how it got there, I do not know. I know it is dead now. To prevent them from coming into the home, use a foundation insecticide. Spray up on the home a few feet and out from the foundation. Turning off the exterior lights around the house helps.

Fertilize your annual flowers and garden one more time. Do not fertilize any trees, shrubs, or roses, allow them to enter their dormant period.

Ymker Greenhouse will have trees and shrubs throughout the summer. The best time to plant a woody plant is in late summer up to 6 weeks before the soil freezes. Keep newly planted woody plants damp allowing them to dry out the top few inches of soil before watering again. A mulch around the tree will help, keep the mulch away from the truck a couple of inches.

Do not forget the Mid Dakota Fair is going on in Winner, SD at the fairgrounds. From Wednesday through Saturday check out their exhibits.