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Year 2000 Diseases and Insects
This has been another interesting year for the gardeners of the area. For the third year in a row, we had above average temperatures during the winter season. We also had fairly decent snow cover during the coldest periods. Because of these factors every pest that we could possibly dread survived. This included many insects and their eggs, every slug, all the spores of our worst fungal enemies and every chipmunk (ground squirrel) and rabbit that has been conceived in the past 3 seasons.
In April, when we were down 3 inches in the annual rainfall and extremely dry, I can remember saying to one of my associates that this was going to be a great spring with very little disease, especially very little apple scab. Then the "May rains" started. Seven inches later, the story had changed. Not only had the fungal deluge begun, but the plants were all showing signs of water stress. The evergreens were the most offended, especially the hollies and yews.
The annual plants were just sitting in the planting beds waiting for oxygen and warmer soil temperatures. The cool season plants faired well, but the warm season crops suffered. We are seeing the results now. At least 3 times a week, I diagnose crown rot or stem rot disease on impatiens. Drenching with a fungicide can often give the plants an edge to recover if the disease has not advanced too far. Use chlorothanil, sulfur or copper.
June was only inch of rain short of May (6 inches instead of the normal 3 for the month) Many plants acclimated well to the excess rain, producing more leaves than usual and putting on much more growth than usual. But many more continued to suffer, especially birches. I have seen lots of chlorosis because of this excess water and resulting lack of oxygen in the soils. It is due to the inability of the roots to metabolize and do their job, so nutrients could not be transported to the developing leaves. One of the best tactics to help plants that have suffered during the growing season is to continue to water throughout the fall, and fertilize after fall color has developed. Roots continue to develop as long as soil temperatures are above 40 degrees. If the plant can develop roots before winter it is ahead of the game for next spring. If (or maybe I should say when) we have another wet spring, the plant already has a higher ratio of roots to top growth and is ready for the new growing season.
Another good habit to develop is to add sulfur to our high alkaline soils in any form, whether it is in the elemental form or a sulfate form. Anytime you lower the pH of the soil it make nutrients more readily available to the plants reducing one area of stress.
The ground dwelling insects and slugs were the most surprising thugs of the season. The populations were so elevated due to the mild winter that it caught all of us off-guard. If someone had not brought in a 3 foot sample of Rudbeckia with sowbug (pillbugs) actually eating holes in the leaves, I would have argued with her that sowbugs only eat organic matter in the soil or only the lower leaves that touch the soil. I also witnessed sowbugs eating the flowers off of pansies. And then there are the slugs. The average length increased to 3 inches this season because they overwintered in ground debris. I actually think that the most damage was from the young ones that hatched from the egg masses laid by the large overwintering slugs ö their numbers have been explosive. Earwigs were the final members of the Ītrio of damageā, eating foliage and flowers of perennials and annuals. Control for all these is a combination of metaldahyde, the slug killer, and carbaryl, an insecticide. There is also a non-toxic product to kill slugs that contains iron phosphate as the active ingredient that has proven to be very effective.
Of the above ground insects that I have seen, the most frequent samples that came in were scales, Euonymus scale and Magnolia scale. Control of these has been tricky due to the timing of the egg hatch. The most effective control is horticultural oil, as it will penetrate the scaleās protective armor. Be cautious about applications when temperatures are above 85 degrees as phytotoxicty can occur.
For control of the leaf feeding insects, like Japanese beetle, use a systemic insecticide with an active ingredient like acephate. The advantage of using the systemic during a rainy season is that it will not wash off. It also kills less beneficial insects, it only kills the insects that actually feed on the plant.
Lawns have looked great through the early part of the season, the excess rain really benefited them. The other advantage of the rainy months of May and June was the even distribution of annual white grub. Very few high density populations have been seen because there were so many "well watered" lawns for the females to lay their eggs, hence they are spread evenly throughout. Use IPM scouting techniques to determine if treatment is necessary. If populations are over 12 grubs per square foot, grub control is necessary to protect from serious damage.
Diseases can be summed up in one word, fungal. I have seen the usual; black spot on roses, apple scab, several rusts, lots of Anthracnose, Cercospora leaf spot, Botrytis bud and leaf blight, and especially now powdery mildew. This late in the season, if the plants have lost less than 25% of foliage, then they should not be compromised. The best plan is to be prepared to protect plants next growing season with protective fungicidal treatments like the systemic forms of Immunox, with myclobutinol as the active, or any systemic fungicide with propriconizol. The key is to begin spraying at bud break to protect the foliage as it develops. Spray weekly during the high pressure months of May and June then every two weeks if conditions favoring fungal growth persist.
Always use the best cultural practices for each specific plant, with the most important one being proper siting. Any time you can keep a plant out of stress, you reduce the chances of insect and disease infestation. The other request that I have is to please pray for a real Chicago winter. That would help to reduce the amounts of the over-wintering insects, slugs, eggs and spores, rabbits, chipmunks and deer. The amazing thing is that the plants have survived these attacks for years, I know that is why I am always amazed by plants. I hope this season has not damaged anyoneās amazement of plants.
Jennifer Brennan, Chalet Nursery, 3132 Lake Avenue, Wilmette, IL (847) 256-0561
Email: chaletnursery@aol.com
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