[Originally featured in the Winter 2022 Issue of UC IPM's Green Bulletin Newsletter]

Weeds can be a problem in any landscaped areas including around trees, shrubs, flower beds, or lawns and turf. As we move from cool weather to warmer temperatures, you will see winter weeds grow and become a problem in established landscape plantings. Effective control of weeds include hand-weeding, hoeing, mulching, and herbicide applications. Good management depends on early attention to where weeds are establishing and adjusting the conditions that allow them to thrive.

Managing weeds in landscape plantings

Each type of planting bed will have specific techniques that work best. In general, dense plantings will shade out most weeds. Regardless of the type of landscape bed, it's always best to control perennial weeds before planting. Herbicides are effective in many types of landscape plantings. They are most effective when integrated with cultural practices. Many of the herbicide active ingredients available for weed control in landscape plantings are only for use by pest management professionals. 

Tree and shrub beds

Landscaped areas made up of trees and woody shrubs don't need as much preplant weed control as other types of beds. Control perennial weeds after planting using methods like mulching, hand pulling, and herbicide treatments. Suppress weed growth by laying down landscape fabric, then adding an inch of mulch on top to thoroughly cover the fabric. If needed, use a preemergence herbicide. Supplement with spot treatments of postemergence herbicides and hand-weeding.

Ground cover beds

Since ground cover is expected to fill the entire bed, landscape fabric is not suitable for weed suppression. Perennial weeds should be controlled before planting. If perennial grasses are encroaching, they can be controlled with selective herbicides like fluazifop, clethodim, or sethoxydim. Spot applications of glyphosate or glufosinate can be used on perennial weeds. Mulch the bed to control annual weeds until the ground cover fills the area. Some hand weeding might be needed.

Annual flower beds

As with other landscaped areas, a dense planting will shade out weeds. Annual weeds can be managed with mulches, frequent cultivation, and hand-weeding. Periodic cultivation (every 3 to 4 weeks) will suppress many weeds. Since nonselective herbicides can't be used after planting annual beds, it's easier to manage perennial weeds beforehand. If cultural methods aren't working to control perennial grasses, you can use grass-selective herbicides with clethodim or fluazifop. Check the product label to be sure that it won't harm the annual flowers in the bed.

Herbaceous perennial beds

Manage weeds in herbaceous perennial beds as you would an annual flower bed. Be sure to get rid of perennial weeds before planting since the bed will be growing for more than one season. Use landscape fabric where possible along with mulches. You might need to supplement with hand-pulling followed by preemergence herbicides. Be aware that fewer perennial plants are included as sites on herbicide labels.

Mixed plantings

A planting bed of a mix of woody and herbaceous plants is a more complex situation. Different areas of the bed might need different treatments. Post-plant herbicide choices are limited so site preparation is critical in this type of bed. Plant woody species first and control the perennial weeds. After the first two growing seasons, add the herbaceous plants. Shade the soil with close planting. Group plants within the bed based on their weed management needs.

Cool weather weeds in landscapes

Blooming Bermuda buttercup next to a residential fence.

Some of the most troublesome weeds in planting beds during late winter and early spring are common groundsel, oxalis, mallows, and nutsedges. 

Common groundsel

Common groundsel is most prolific in cool weather, germinating from seeds this time of year. This weed produces many seeds and can rapidly infest landscape beds. It is best controlled before it flowers. Mulch is highly effective at controlling common groundsel. Young plants can be hoed out. Diquat or glyphosate-based herbicides will control common groundsel in landscape beds. 

Mallows

Mallows are annual weeds that begin growing with the first rains so you may already be seeing these sprouting up in landscape beds. This plant develops a long taproot so it should be pulled when it has four or fewer true leaves. At least three inches of mulch is needed to suppress mallow. Young mallow plants might be managed with 2,4-D products, but this herbicide will injure broadleaf plants growing nearby.

Nutsedges

Purple and yellow nutsedge are perennial plants that sprout in spring from tubers. Remove these weeds as soon as possible to prevent tuber production. Tubers (sometimes referred to as “nuts” or “nutlets”) are key to nutsedge survival. Once established, nutsedge plants are difficult to control. They don't grow well in shade so dense plantings of ground cover or shrubs will suppress nutsedges. Few herbicides are effective at controlling nutsedge.

Oxalis (creeping woodsorrel and Bermuda buttercup)

While Oxalis (creeping woodsorrel) can bloom almost any time during the year, spring is a time of heavy flowering and seed formation. Buttercup oxalis sprouts in fall and is a major weed in ornamental plantings. Hand pulling can control these weeds but be aware that mowing can spread creeping woodsorrel. Landscape fabric with two to three inches of an organic mulch on top can control oxalis. There are no selective postemergence herbicides for creeping woodsorrel in ornamental plantings.

Herbicide injury

Desired plants could be injured when herbicides are used in established landscape beds. Herbicide damage symptoms vary depending on the herbicide and the plant. Symptoms can include yellowing, bleaching, distorted growth, and death of leaves. Avoid herbicide injury by following the label about the site, plant, and application rate. Granular formulations are less likely to damage plants than sprays. When using a nonselective liquid herbicide, apply on a calm day using low pressure and large droplets. Use a shielded sprayer to avoid contact with nontarget plants. If plants are injured from soil-applied herbicides, the damage is often temporary but can cause growth inhibition. Adding organic amendments and keeping the soil moist will help the herbicides to break down faster.

For more details and for information about weed management before planting a landscape bed, see Pest Notes: Weed Management in Landscapes.

Emerald ash borer. Photo by Howard Russell, Michigan State University, Bugwood.org

Invasive pest species threaten California's natural environment and can have an impact on public health. Help spread the word about these invasive species and how to limit their introduction, spread, and harm. Learn to recognize these pests and distinguish them from look-alikes. If you suspect you have found any of these species, contact your local County Agricultural Commissioner or report it to the CDFA Report a Pest Hotline.

Emerald Ash Borer

The emerald ash borer (or EAB) is an invasive insect that has been found for years in numerous states across the country, but until recently had not been found on the West Coast. In June 2022, EAB was detected in Oregon. This insect feeds on all species of ash trees and has the potential to devastate whole communities of trees.

See the California Department of Food and Agriculture website for information about its biology and national distribution.

Spotted lanternfly adult. Photo by Pennsylvania Department of Agriculture, Bugwood.org

Spotted Lanternfly

In California, we've been on the lookout for the spotted lanternfly (SLF) for several years. In July 2022, a truck carrying firewood into California from New Jersey (silly, I know!) was inspected at a CDFA Border Inspection Station in Truckee and the wood was found to be carrying egg masses of SLF. The wood was destroyed but this is a significant detection.

Understand the danger of moving firewood from place to place within the state and especially across state borders. Firewood can harbor many types of invasive pests including SLF but also invasive shothole borers, gold-spotted oak borers, and other very hard to see invasive insects AND diseases.

Jumping worm/crazy worm

The invasive jumping worm (Amynthas agrestis) has many common names: Alabama jumpers, Jersey wrigglers, wood eel, crazy worms, snake worms, Asian jumping worm, and crazy snake worms. The jumping worm has been found in Napa and Sonoma Counties. It is similar-looking to the common earthworm but thrashes wildly and is said to jump as much as 1 foot off the ground.

Jumping worm. Credit: Wikimedia Commons.

Like other earthworms, jumping worms eat fallen leaves and other natural material on the ground. However, these worms are voracious eaters. They eat so much of the soil “litter” layer that they nearly clear the top soil of all life. Many plants can't grow or spread without this layer of leaf litter, plus this disrupts the ecosystem of the leaf litter.

Read more about this worm in this article by Oregon State University. UC IPM is compiling information about the worm and where it has been found in California and will publish and announce this information once finished.

Stay Informed

There are many other invasive species in California being monitored for state agencies and many others receiving management efforts. Be sure you are subscribed to the UC IPM Home & Garden Pest Newsletter and social media platforms (@ucipmurban) to ensure you are receiving timely updates and news.

Other useful resources for these invasive pests and many others:

UC IPM Invasive and Exotic Pests web page

Center for Invasive Species Research at UC Riverside

Urban & Community IPM webinars https://ucanr.edu/sites/ucipm-community-webinars/ 

CDFA target pest web page https://www.cdfa.ca.gov/plant/PDEP/target_pests.html

[Originally published on the UC Master Gardener Program Statewide Blog on January 10, 2023]

A flooded backyard in Elk Grove, Calif. following exceptional amounts of rain in January. Taking steps to improve drainage and reduce water damage following flooding is crucial to the health of your plants and lawn. Photo credit: Erica Schroepfer, used with permission.

Proper irrigation and drainage are critically important for the health of plants and trees. But what happens when Mother Nature throws an atmospheric river curveball, and your yard or garden is now under water from heavy rains or floods?

Good garden soil contains a network of pore spaces filled with water and air. Both are necessary for healthy roots and beneficial soil-dwelling organisms. When the pore spaces fill with water, air is no longer available to the root system, and the roots become susceptible to root-rot organisms. Understanding the effects of flooding on plant health and caring for them after a flood event is important to saving your plants and garden.

Once the floodwaters have receded, assess the damage to your garden and begin the recovery process. There are a few things you can do to minimize the damage to your plants from flooding:

1. Remove any debris, such as mud and silt, that may have shifted and accumulated on your plants. 
   
   
2. If the soil is waterlogged, improve drainage by digging ditches or furrows to redirect water away from plants. 
   
   
3. Check the soil for compaction and loosen it up with a garden fork. This will help to improve drainage and make it easier for water and nutrients to reach the roots of your plants. 
   
   
4. Wait until the soil dries out before working with it in order to reduce additional compaction. Avoid walking on waterlogged soil to prevent compaction and further root damage. Stay off a boggy lawn!
   
   
5. Inspect your plants for damage to the roots, leaves, and stems. Remove any damaged parts, and prune your plants back to healthy growth if necessary.
   
   
6. Remove contaminated material. Consider that any garden produce touched by floodwater may be contaminated and discard it. While the risk of contamination is low in residential areas, runoff from septic systems, pastures, or industrial areas can carry potentially harmful microbes and chemicals.
   
   
7. Monitor your plants closely for signs of stress, such as wilting or discoloration, and address any issues that arise as soon as possible.
   
   
8. Once dry, start to water your plants gently and gradually to help them acclimate to the new soil conditions. 

Connect with your local UC Master Gardeners! 

Recovering from a flood can be a difficult and time-consuming process, but with proper care and attention, your garden can recover and thrive. The UC Master Gardener Program is available to help! For gardening questions and local county resources, click here to Find a Program. You will be redirected to your local county website and contact information. 

Source: Flood: Plant Stress in Extreme Wet Conditions, https://marinmg.ucanr.edu/PROBLEMS/EXTREME_CONDITIONS/Flood/

Avoid walking on waterlogged soil to prevent compaction and further root damage. Stay off a boggy lawn! Photo credit: Erica Erica Schroepfer, used with permission.

Credit: Steve Garner, Flikr.

An immense amount of rain has fallen across California in recent weeks. While rain is incredibly beneficial, in excess it can cause serious problems. The continued wet conditions opens the door for many pests, so see the list of dos and don'ts below for common wet weather pest prevention tips.

DO

• Check for snails and slugs. These critters thrive in moist environments and can often be seen on sidewalks and driveways after rain. Their feeding causes irregular holes on leaves and flowers, and they'll leave behind a slimy trail. Pesticide sprays and dusts will not be effective under such wet conditions and therefore, should not be used. Instead, hand pick them or trap them using a wooden board trap.
• Remove weeds and unwanted plants. When the ground is wet it is much easier to pull weeds and remove unwanted plants from your garden or landscape. Use this time to your advantage by catching up with any winter annual weeds, like oxalis, nutsedge, and groundsel. Be on the lookout for more in the coming weeks.
• Dump standing water. As the weather warms, any areas left with standing water will be a breeding zone for mosquitoes. This wet winter is already favoring a big mosquito season, so do your part to reduce habitat around your home. This can include dumping flowerpots and saucers, wheelbarrows or buckets, and cleaning clogged storm drains or gutters.
• Continue to conserve water. During the fall and winter months, adjust your irrigation schedule to reflect the increase in rainfall. Consider purchasing a rain sensor for your sprinkler system to avoid irrigating while it is raining. Overirrigating your plants during this time can lead to root rots and other water-borne pathogens so do what you can to reduce excess water.
• Be on the lookout for ants, cockroaches, and earwigs. These insect pests may invite themselves into your home when flooding or heavy rains make it unfavorable for them outside. Seal any cracks or openings in your home to prevent them from coming indoors. Use weatherstripping and door sweeps, and place sticky traps near entryways. Keep food sealed tightly and maintain a clutter-free environment to prevent these pests from establishing indoors.
• Remove mushrooms. Wet weather encourages the growth of above ground fruiting bodies of fungi. While not harmful to your garden or lawn, you may want to remove mushrooms to prevent children and pets from consuming them.

 DON'T

• Fertilize your garden, lawn, or outdoor potted plants. Any fertilizer applied now will likely be washed off the ground or rapidly leached out of the soil and into our waterways. Wait until the winter storms have passed and there is a stretch to time between days with rain.  
• Use pesticides (sprays, dusts, drenches). Similar to fertilizers, these products are more likely to just contaminate waterways than control any pests. Pesticides applied to foliage as sprays will be washed away quickly with daily rainfall and those applied to the soil as a systemic drench will likely not be taken up by the plant in waterlogged soils and instead will become runoff. Pesticide dusts need to remain dry to be effective, so now would not be the time to use those outdoors either.
• Prune plants. Unless necessary to remove damaged limbs or branches from the recent windstorms, avoid pruning plants under wet conditions. Pruning at this time can make plants vulnerable to pathogens and easily spread disease from one plant to another. Apricots, cherries, and olives should never be pruned during cool, wet conditions. 
• Worry about tiny piles of soil. Earthworm activity is increased during rainy weather, so if you are seeing piles of soil on top of landscape beds or the lawn, don't worry—it's just the earthworms coming out and getting some air. As they do this, they help aerate the soil. Earthworms deposit castings when they ingest soil and leaf tissue and emerge from the soil surface to remove fecal matter. Castings are rich in nutrients and organic matter and can provide some benefits to turfgrass plants.
• Compact your soil. Avoid driving or excessive walking on soft ground and keep heavy machinery off wet soils. Compacted soils make lawns, trees, and shrubs more susceptible to diseases, drought, and insects as they restrict oxygen and water from plant roots.   

For year-round actions to keep landscape plants healthy, reduce pest problems, and prevent future issues, see the Seasonal Landscape IPM Checklist to find monthly activities specific to your county or region.