While we hope your flowerbed is always healthy and in full-bloom, damaging diseases and insects can pop up unexpectedly. Here are some to look out for in your gardens.
Aster yellows disease is spread by a small leafhopper insect. The population of leafhoppers dramatically increases shortly before the wheat crops are harvested in mid to late June. Check plants in your garden for the disease beginning around the first of July. Note the proliferation of mutated vegetative growth around the flower bud. There is no cure or treatment for the disease. You should remove infected plants immediately from your property and do not place into a compost pile. Read the K-State publication on aster yellows disease for more information and a list of susceptible cultivars.
Thrips are extremely small insects that are difficult to see. Most often a distortion of the growing tips and flower buds are the first signs of their presence. Insecticidal sprays are effective in controlling the insect. Angelonia and vinca are useful as indicator species for the presence of thrips.
The larva, caterpillar stage, of a small moth's lifecycle feeds on the flower petals of several annual flower species. Petunia, geranium and calibrachoa are favored hosts. Damage from the bud worms seems to appear overnight. Plants that are beautifully flowering all of a sudden have no flowers. The insects have two to three lifecycles per growing season and can easily be controlled with insecticides. We apply a spinosad-containing insecticide on our flower trials to keep these pests in check.
These pests seem to be increasing each year, and we find them congregating on the cannas and roses in the flower trials. The large beetles are easily seen while voraciously feeding on a wide variety of garden plants. KSUTurf's blog post about Japanese beetles has great information on the insect and various control methods.
Rose rosette disease causes unusual growth in roses like elongated stems, thick stems, excessive thorns, and other abnormalities. There is no cure for this disease, and you should remove plants, roots and all, from your garden and sterilize any tools that may have been in contact with an infected plant. Read K-State's publication on Rose Rosette for more detailed information.
We run the annual and perennial flower trials for Kansas State University