Hot weather brings insect and disease problems

Question: Attached are some pictures of little green bugs on my roses. Some of the rose leaves also have mildew on them. I am also concerned about needles with mottled yellow color on my dwarf pine shrub. Should I spray something for these problems?

Answer: Thanks for sending pictures of your problems. That helps a lot in solving them. The insects on your roses are aphids. The mildew on the rose leaves is caused by a fungus disease. The mottled leaves on the pine shrub are probably caused by spider mites. Spider mites are very tiny insects which almost require a hand lens to see them. They often make tiny webs like I see in your picture.

Fortunately there are some good safe organic control pesticides for all three of your problems and many other common insect and disease problems.

Insecticidal soap is very effective in removing both aphids and spider mites from plants. It is best applied with a hose attachment or other sprayer which has strong washing action. The soap loosens the insect’s attachment to the plants. Once they are on the ground they cannot return to plants.

Neem oil is an organic pesticide which controls both insects and foliar diseases. It will control mildew and rust as well as aphids on roses. Neem oil is also toxic to bees if sprayed directly on them, so it should be applied in the late afternoon when bees are not active.

If you notice holes in leaves, two other organic insecticides are effective on chewing insects. Bacillus thuringensis (sold as Thuricide or Dipel) is very effective on worms on cabbage, broccoli, cauliflower and other cabbage family vegetables.

Spinosad is effective on a variety of chewing insects. I use it every two weeks on apples to prevent worms.

It is important to spray plants thoroughly. Most insects feed on the bottoms of leaves. I try to point the spray up so that I cover the bottom of foliage. Most pesticides only kill adult insects. A second application should be made in about two weeks to catch the next generation of developing insects.

Slugs and snails also chew leaves. They are best controlled using bait. Slug bait containing iron as the active ingredient is safe to use around children and pets.

These organic pesticides are seldom available at big box stores. Nurseries and garden centers usually carry them. All are available online.

Allen Wilson can be contacted at