- (Focus Area) Pest Management
- Author: Cheryl A. Wilen
Nurseries and garden centers often sell a wide range of plants for use in gardens and landscapes. As a consumer, you may manage a complex array of different landscape plantings, including woody trees and shrubs, woody ground cover beds, annual flower beds, herbaceous perennial beds, and mixed plantings. This complexity often makes weed management difficult. An integrated approach is the most economical and efficient way to control weeds, so knowing strategies for managing weeds in a variety of landscapes can help.
Woody Trees and Shrub Beds
Control perennial weeds before planting, although weed control can also be done after planting. Densely planted areas will reduce weeds. Geotextile (landscape) fabrics rather than black plastic used with a shallow layer of mulch will keep weeds from emerging. If you mulch without a geotextile base, the mulch layer must be thicker to prevent weed emergence.
If needed, you can use a preemergence herbicide to control annual weeds and supplement with hand weeding and spot applications of postemergence herbicides for weeds that are not well-controlled by hand weeding, such as perennial grasses.
Woody Ground Cover Beds
Mature, woody ground cover beds should exclude most weeds; however, when ground cover is just establishing, weed growth is likely. Perennial weeds must be controlled before planting, although perennial grasses may be selectively controlled after planting with a grass-selective herbicide like sethoxydim (Grass-Getter). Annual weeds may be controlled with mulch plus a preemergence herbicide but rooting of stolons in new plantings may be affected. You will need to supplement with some hand weeding.
Annual Flower Beds
A dense planting in annual flower beds will help shade out and compete with many weeds. Flower species should be carefully selected for weed management compatibility. Periodic cultivation at 3- to 4-week intervals and between flower beds plant rotations will also suppress weeds. Perennial weeds must be controlled before planting. Annual weeds can be controlled with mulches, preemergence herbicides, frequent cultivation, and/or hand weeding. Control perennial grasses with grass-selective herbicides like clethodim, sethoxydim, or fluazifop. Avoid nonselective herbicides in annual flower beds after planting.
Herbaceous Perennial Beds
Weed management options in herbaceous perennial beds are similar to those for annual flowers, except that it is more important to eradicate perennial weeds as there will be no opportunity to cultivate or renovate the bed for several years; and fewer species are included on herbicide labels. Geotextiles may be used in these types of plantings. Manage weeds with mulches and supplement with hand weeding. If needed, use preemergence herbicides after hand weeding.
Mixed Plantings of Woody and Herbaceous Plants
Weed management in mixed plantings is complex because of the diversity of species. Different areas of the bed could receive different weed treatments. Site preparation is critical because post-plant herbicide choices are few. Plant the woody species first and control perennial weeds in the first two growing seasons, then introduce the herbaceous species. Plant close together to shade the soil. Group plants within the bed that will receive similar weed management programs.
In most landscape situations, herbicides should not normally be needed by home gardeners. Mulching, removal by hand, and proper irrigation (pattern and amount of water) are sufficient in most cases. Find more information in the UC IPM Pest Notes: Weed Management in Landscapes.
Last week, someone called our helpline about a strange phenomenon happening on her backyard plants. She described the symptoms as “big, white, masses of fluffy cotton.” I asked her to email some photos our helpline address (email@example.com).
When I opened her email, I was surprised to see images of what appeared to be giant whiteflies. This pest invaded California in the early 1990's and was until recently only found in Southern California and along the coast. The Stanislaus County Agricultural Commissioner's Office confirmed that giant whiteflies are present in our County.
If you've heard of whiteflies or dealt with them in your landscape, you may wonder how giant whiteflies are different, aside from being larger. Both pests suck plant juices and weaken plants. The main difference is that giant whiteflies tend to feed together in large groups. This large population creates waxy looking deposits that create a “bearded appearance” or what the caller described as “fluffy cotton” on plants. If you look closely at the infestation, you may see the pests living on the undersides of the leaves.
If you find giant whiteflies in your landscape, there are a few things you can do. For small infestations, pull off affected leaves, place them in a sealed bag, and discard them. For larger ones, direct a strong stream of water at the undersides of the leaves to knock giant whiteflies off and kill them.
Visit the UC IPM publication Pest Notes: Giant Whitefly for more information about this pest, or call our helpline at (209) 525-6802 to speak with a UCCE Master Gardener.
In Part I, we discussed why mosquitoes bite, and which mosquito species can spread West Nile and Zika virus. Now, let's talk about what mosquitoes need to reproduce, how to prevent them from breeding around your home, and best methods to protect yourself and your family while outdoors.
What do Mosquitoes Need to Breed?
The mosquitoes that spread West Nile virus and Zika need water to lay their eggs. Female mosquitoes can lay their eggs in even the smallest amount of water. Places in your yard that appeal to them include standing water found in ponds, garden pots, children's toys, or even pet water bowls. Eliminating these possible breeding spaces is key to mosquito control.
Watch the video “Don't Let Mosquitoes Breed in your Yard” from UC IPM for helpful tips.
Protect Yourself from Mosquito Bites
There's a plethora of mosquito control and prevention items for sale, but many are ineffective.
When outdoors, protect your skin by wearing long-sleeved pants and shirts, long socks, and a hat. Be aware that mosquitoes can bite through a thin layer of clothing. Also, choose and apply an effective EPA-registered mosquito repellent that contains DEET, picardin, IR3535, or oil of lemon eucalyptus to exposed skin.
You may be tempted to use outdoor sprays to battle mosquitoes. However, this method is only temporary and doesn't help control the source of the problem. The best way to avoid bites are prevention and protection.
Resources: UC IPM Pests in the Urban Landscape. Zika, Mosquitoes, and Repellents. https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=21923
You've probably read a lot lately in the news about West Nile virus and Zika virus. In mid-June, the first human case of West Nile virus in Stanislaus County was diagnosed. This past week, mosquitoes that can carry the Zika virus were found in our county.
Why do mosquitoes bite?
It may surprise you to learn that mosquitoes get most of their food from flower nectar. However, female mosquitoes need a blood meal to produce eggs. If she bites someone while carrying a virus, it can infect that person.
What is the difference between West Nile virus and Zika virus?
West Nile virus is carried by Culex tarsalis or the Western encephalitis mosquito. This species is most active just after sunset. It feeds on birds and other mammals, including humans.
Eighty percent of people infected with West Nile virus do not show symptoms. The other twenty percent may have mild symptoms including fever, headache, body aches, nausea, vomiting, and sometimes swollen lymph glands or a skin rash. One in 150 people infected will develop a neurological illness that may result in death.
Zika virus is transmitted by several species of Aedes mosquitoes. These mosquitoes bite people during the day. Women infected with Zika during pregnancy may have an infant born with microcephaly and other severe brain defects.
Although this mosquito has been found in Stanislaus County, the virus has not been found in California. Aedes mosquitoes can only transmit Zika if they carry the virus.
How can I protect myself and my family?
Stay tuned tomorrow for part II of this blog post, with helpful tips for prevention and protection from mosquitoes.
University of California Agriculture and Natural Resources. UC IPM Pest Notes: Mosquitoes. Taken from http://ipm.ucanr.edu/PMG/PESTNOTES/pn7451.html on August 5, 2019.
Vector Disease Control International. Culex tarsalis-the Western Encephalitis mosquito. Taken from http://www.vdci.net/blog/mosquito-of-the-month-culex-tarsalis-western-encephalitis-mosquito on August 5, 2019.
California Department of Public Health. Zika: What Californians Need to Know. Taken from https://www.cdph.ca.gov/Programs/CID/DCDC/Pages/Zika.aspx on August 5, 2019.
Over the past few months, gardeners have asked the UCCE Master Gardeners for help with their grapes. They want to know:
- What's this white powdery substance on my grape plants?
- Why are my grapes so small?
- What's causing my grapes to split?
- What can I do to “save” my grape plants?
The culprit is a common grape disease called powdery mildew. This fungus leaves a telltale white powdery coating on plants. It also deforms leaves, shoots, and grapes. Young grapes can be stunted or scarred, and sometimes split open.
We've told gardeners that unfortunately, powdery mildew can't be eradicated. For now, gently hosing down plants weekly with water will help to wash off and kill the spores.
In winter, prune grapes and remove and destroy infected materials. During spring, use fungicides to protect grapevines. Timing is important. Read about how and when to prevent and control this disease in the publication Pest Notes: Powdery Mildew.
Small grapes are a result of too many clusters of grapes on a vine. The clusters will need to be thinned. Sometimes gardeners have trouble doing this. It may feel like you are throwing away perfectly good fruit! However, thinning out grape clusters is a necessary task that should be done in early spring during the first three to four weeks after fruit has set.
Study up on grapes now! Then you'll know what you need to do next year. For information on pruning, thinning, and growing grapes, visit The California Garden Web page Growing Grapes in Your Backyard.