Roots, Shoots, Fruits & Flowers: Powdery Mildew, Toxic Nandina & Wolf Spiders

If you want to contact Roots, Shoots, Fruits and Flowers, please send your questions and pictures to Keith Hawkins, Area Horticulture Agent (AHA), 337-463-7006 or Also, you can be on the “green thumbs” email list by emailing your request to the address above.

“Before you buy or use an insecticide product, first read the label, and strictly follow label recommendations. Mention of trade names or commercial products in this article is for informational purposes only and does not constitute an endorsement by Louisiana State University AgCenter.”

“This work has been supported, in part, by the USDA National Institute of Food and Agriculture, Renewable Resources Extension Act Award, Accession Number 1011417.”


Cucurbit with powdery mildew. Photo: Vegetable Crop Hotline.

Powdery Mildew

Peggy, a beekeeper, shared this concern by email, “I have pumpkins, squash, and cucumber plants that have leaves covered in white powdery stuff. What can we spray on them that is bee friendly?”

Peggy probably has powdery mildew, and the vegetables she listed are in the cucurbit family. Lee Rouse, an AgCenter horticulture agent, wrote in an online article, “Powdery mildew will develop white powdery spots on both leaf surfaces and expand as the infection grows. The leaves will eventually turn yellow or brown and fall off, exposing the plant or fruit to sunburn. In some cases, powdery mildew will cause the leaves or shoots to become twisted or distorted.”

Rouse makes these recommendations for control, “[Mildews] can be managed successfully by planting resistant varieties in areas of the garden with full sun and good air movement. Plants can be protected with synthetic chemicals or biopesticides.

As with most diseases and insects, prevention is the best method on control. Many practices can help to prevent these diseases from the beginning, such as planting in full sun. This will help to dry off the leaf surfaces quickly as to not spread the disease through water droplets sitting on the foliage. Be sure to keep the garden well mulched as well as provide proper spacing between plants to allow sunlight and air flow through the crop to help dry the foliage. Be sure to avoid watering in the evening. Setting an irrigation time for early in the morning or setting out the hose and the sprinkler the evening before so you only must turn the spigot on in the morning are great ways to get water to the garden early in the morning.

Overfertilization can also cause an outbreak of both powdery and downy mildew. Instead of using a granulated fast-release fertilizer, consider using a slow-release product. Slow-release fertilizers come in many forms, such a compost, manures, and resin-coated fertilizer, such as Osmocote.”

AHA also shared these notes with Peggy, “Copper fungicides can be used in organic gardening for PM. After reading the label for a copper fungicide, the biggest environmental hazard is runoff because this fungicide is toxic to fish and invertebrates like crawfish. As near as I can discern, copper is safe for bees.”


Leaves and berries of a nandina plant. Photo: LSU School of Veterinary Medicine.

Toxic Nandina

Lea emailed a short note, “I did not know this. True?” and included a link to a Facebook posting about how the berries of nandinas are toxic to songbirds.

First, Lea asked a responsible question because there is some much false information on the internet. AHA consulted with Dr. Ashley Long, an AgCenter wildlife biologist, about nandina toxicity and songbirds. Dr. Long confirmed the toxicity of the nandina berries, “The berries are toxic to all animals, but aren’t a preferred food. The deaths that are reported for birds generally occur when other food sources are low, and the birds consume enough to cause hemorrhaging. I have read some articles that suggest cyanide levels in the berries are higher during periods of drought, making them more toxic to birds if consumed during drought conditions.

The deaths are most often reported for cedar waxwings, northern mockingbirds, and American robins, in part because these species eat berries, but there is probably some reporting bias here too – these three species are larger, abundant, and common in urban areas/neighborhoods, so people are more likely to notice them if there is a mortality event.”

[It is] Hard to know the full extent of the issue, but [it] certainly cannot hurt to promote native plants for this and many other reasons!”


An image of a wolf spider. Photo: Caroline Coleman, Ragley, LA.

Wolf Spiders

Caroline wanted to share an image of a discovery and wrote in her email, “[I} Wanted to share with you a photo of this huge wolf spider I found on my property out in Ragley. I found your email on the LSU at the website. It measures about 2 inches. Huge!!” This image shows a large spider under clear plexiglass and includes the use of a tape measure to give a sense of scale to this picture.

Mike Merchant, an insect specialist at Texas A&M University, shared this information in his Extension blog, “Wolf spiders are hunting spiders. This means they do not sit passively on their web but go out and search for food. Unlike their namesakes, they do not necessarily chase down prey, but go to a likely location and wait for a tasty insect or other small arthropod to come along. When things get slow, they pick up and move to a new location. According to Richard Bradley’s Common Spiders of North America, there are at least 238 different species of wolf spiders in America north of Mexico. They can be found in just about any habitat, from the beach tidal zones to the highest mountaintops. Most wolf spiders are nocturnal, coming out at night to hunt.”

6/11/2021 1:20:00 PM
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