Serious whitefly infestation and powdery mildew

Asked May 9, 2018, 8:58 AM EDT

Hello, I have two major problems that I need help with: 1.) In the past two years, my garden has become infested with whiteflies. At first, they were just out back in my herb and vegetable garden, but they have spread throughout my whole property and last season were also on perennials out front of my house and even, I believe, in the grass. I had started spraying insecticidal soap on affected plants, but it was too much to keep up with. I would've needed to spray three times a week and buy a gas powered sprayer because of the large area. 2.) I have a powdery mildew problem that has also grown worse and worse in the last three years. It was so bad two years ago that I decided not to plant any vegetables this past year so I wouldn't have to be disappointed about them failing. I had sprayed the vegetables and lilacs with Actinovate a few times and even treated the soil a few times, but the plants still got moldy. I have a long strip of peony's on the side of my house(25 ft.) that I have had to cut down after the bloom for the last two years because of the mildew. I can't provide any photos yet, as the season is just beginning, but I have seen some whiteflies around already. Any help you could provide would be appreciated. You are welcome to call at the number below if you prefer or have additional questions. Thank you!

Baltimore County Maryland

1 Response

Here is some information on whiteflies and powdery mildew.
For vegetables look at our pest profile on white flies. There you will see most common greenhouse vegetable host plants for whiteflies. There are some native whiteflies that may overwinter. Usually whiteflies do not overwinter outside in MD but can overwinter inside in heated greenhouses. If you are buying transplants be sure to check the transplants carefully for insects. See our vegetable website for more information on whiteflies

We do not have a specific list for ornamentals but you may see them on some houseplants and annuals.

Powdery mildew has become a bigger problem on peonies the past few years. Make sure there is adequate sunlight and good air circulation to reduce humidity levels. Allow proper plant spacing for the same reasons. Pruning for better air circulation also may help. Practice good sanitation.

Cut down all infected foliage this fall as soon as frost turns it brown (or before if the mildew has killed it.) Get rid of this infectious material. Next spring, monitor your peonies, and as soon as you see one infected leaf, pull it off. You will have to decide it you want to spray a fungicide or a horticultural oil labeled for powdery mildew or tolerate it. Fungicides are preventative--not curative. They will halt further infection, but cannot restore infected leaves to health. There are no resistant peony varieties on powdery mildew. Here is our website info on powdery mildew

Take a look at our website on powdery mildew on vegetables -
Treating the soil will not cure powdery mildew.

Lilacs can be susceptible to powdery mildew, a fungal disease. This fungal disease is usually not lethal to lilacs, but is certainly not attractive. Control begins by selecting powdery mildew resistant varieties.

Check the label registration on horticultural oil products for powdery mildew control listings. If severe, you can spray once a month as soon as you notice the mildew. However, this disease will not kill the plant and you do not have to spray. Make sure there is good air circulation and is located in full sun.

You can send us photos as soon as you notice syimptoms on your plants.