You may be noticing white grubs in your compost piles, lawns, or garden beds. These white, c-shaped critters can be 1/4 inch long or 2 inches long, depending on the species. White grubs are the larvae of some scarab beetles, and though many of them can cause damage to our landscapes, not all of them do.

There are three species that feed on the roots of grasses, making them a potential pest to lawns when in high numbers. These species may also be found in landscape or garden beds that are near grassy areas or were recently converted from grassy areas. Compare the size of white grubs you may find, as some species are much larger or smaller than others and can help you determine which is present.   

• The larvae of masked chafer beetles are 1 inch long with dark heads and six legs. Adult beetles are golden brown and can be seen flying around in the evening hours.
• Billbug larvae are 3/8 inch long, also with dark heads andwhitebodies, but these grubs lack legs. Adults are brown weevils.
• Black turfgrass ataeniusls larvae are 1/4 inch long– much smaller than masked chafer grubs. Adult beetles are black and shiny.

One of the largest species of white grubs you might find in California are of the green fruit beetles, also known as figeater beetles or June beetles. The grubs of these beetles can be up to 2 inches long and are commonly found in compost piles, or near ripe and rotting fruits– which they feed on. These grubs, however, won't usually damage your landscape or garden plants. The adults are very large, metallic green beetles that are often mistaken for the invasive Japanese beetle, which is much smaller and, for the most part, is not found in California.

In most cases, the presence of white grubs does not require treatment and populations of 6 or less per square foot can be tolerated. If you notice them in your garden beds, they can be hand-picked and killed. Some may choose to feed them to their backyard chickens or leave them out for the birds. When infestations of grass-feeding white grubs occur, the lawn may feel soft and spongy, sometimes able to be rolled back like carpet. You may also notice animals like raccoons and moles digging in your yard, looking to snack on some white grubs.

To learn more about identifying and managing white grubs, see Pest Notes: Lawn Insects.

Curious about composting but not sure where to start? Tried composting in the past but gave up for various reasons? In this free class from the UC Cooperative Extension Stanislaus County Master Gardeners, you will learn how to turn kitchen and garden waste into "gold" that you can use in your garden. Adding compost to your houseplant pots, landscape, or garden is extremely beneficial. We will review common problems and their solutions. The main thing to remember that no matter what you do, "Compost happens!" One lucky person from each class will take home a free composter!

Stanislaus County Library Composting Classes

Tuesday, September 6, 2022 at 6:00 p.m. – Salida Library
Saturday, September 10, 2022 at 2:00 p.m. – Riverbank Library
Monday, September 12, 2022 at 6:00 p.m. – Ceres Library
Tuesday, September 20, 2022 at 6:00 p.m. – Oakdale Library
Monday, September 26, 2022 at 6:15 p.m. – Modesto Library
Wednesday, September 28, 2022 at 6:00 p.m. – Turlock Library

Stanislaus County Agricultural Center, Harvest Hall Composting Class

Tuesday, September 27, 2022 at 6:00 p.m. rooms D&E

Turlock Community Gardens

We taught composting at this location in spring, so this month we are offering vermicomposting, the fun and easy way to compost kitchen scraps using red wiggler worms. Children are welcome!

Saturday, September 17, 2022 at 9:00 a.m.

Patterson Library

We are offering a Fall Vegetable Gardening Class at the Patterson Library, in case you missed this class last month at      other locations. Class is Wednesday, September 14, 2022 at 2:00 p.m. Composting will be taught at the Patterson Library on October 12 at 2:00 p.m.

Never miss a class, bookmark our online calendar: https://ucanr.edu/sites/stancountymg/Calendar/

Upcoming Compost Connector Webinar

 

Looking for financial assistance in bringing more compost to your farm? 

Then consider attending a webinar on Wednesday 8/24 from 10:00am - 11:30am with Zero Foodprint about theirCompost Connector program, which helps agricultural producers get discounted compost! You'll learn about the funder and program requirements and receive a step-by-step demonstration on how to apply.

While the webinar is being hosted by San Diego RCD, the information presented will be relevant for all of California.

You can register here, and also see the attached flyer. Feel free to share this with your networks and fellow farmers and ranchers, and we hope to see you there!

Since Fall 2020, I have been evaluating the effects of applying green waste compost on established alfalfa. The three-year project includes two trials – one in the San Joaquin County Delta and the other in Yolo County – and is a collaboration with Rachael Long (UCCE) and Radomir Schmidt (UC Davis). The project is supported by a CA Department of Food and Agriculture Healthy Soils Program (CDFA HSP) demonstration grant. Our interests are in evaluating whether compost enhances soil carbon and nitrogen storage, improves soil physical characteristics (i.e. improved water infiltration, reduced compaction), reduces greenhouse gas emissions, and/or boosts alfalfa yield.

Compost is decomposed organic matter from plants or animals and may be classified by the carbon-to-nitrogen ratio (C:N). The C:N is the relative amount of carbon and nitrogen in the material. Plant-derived composts (like green waste compost) have a high C:N, and animal-derived composts (like composted manures) have a low C:N. A material with a ratio greater than 30:1 is considered a high C:N material. The ratio is important because it affects microbial metabolic functioning and plant-available nitrogen. Both high and low C:N composts promote soil functioning by increasing soil carbon that is in a form easily accessible to microbes. That, in turn, can improve soil biological activity and physical conditions. With a high C:N material, however, nitrogen may be immobilized (“tied up”), so soil nutrient monitoring is important in order to stave off impacts to crops.

The San Joaquin County trial is approximately 20 acres, and there is no history of compost application at the site. The soil is a Peltier mucky clay loam that is considered partially to poorly drained. Compost applications are surface-applied in the fall/winter to plots that are two border checks wide (120 ft) and approximately 1000 ft long. Two green waste compost rates – 3 tons/ac and 6 tons/ac – are being compared to the untreated (non-composted) control. The first compost application was made in Fall 2020 following the first cutting season of the alfalfa stand. The second application was made in Winter 2021, and the final will occur in fall/winter 2022. Baseline soil samples were collected at the beginning of the study (October 2020), and annual sampling is done every fall season before compost application. Alfalfa yield is assessed 3-4 times per year by taking quadrat samples from the grower's windrows. Greenhouse gas samples are collected on a monthly basis.

Preliminary results. Yield was measured from three cuttings in 2021, and so far, from two cuttings in 2022. (We anticipate measuring yield from two more cuttings in 2022.) Our preliminary results from these five cuttings indicate that compost can improve alfalfa yield over the untreated control but that a rate of 6 tons/ac does not improve yield over the 3 tons/ac rate (Fig. 1). We are also testing forage quality, and those results will be available in the fall.

I recently held a field day at the trial location. If you were not able to make it, please visit my website for the handouts. The handout “Compost for Soil Improvement in Alfalfa” shows other preliminary results from this trial, including soil carbon and nitrogen and greenhouse gas emissions. In addition, there are handouts describing other organic matter amendments in alfalfa and forages.

Figure 1. Preliminary yield results over five cuttings in 2021 and 2022. The compost rate of 3 tons/ac improved alfalfa yield over the untreated control.

Conclusions. Organic matter amendments, as from compost, can improve soil functioning, but changes take time to observe, let alone be realized financially. We estimate that compost (material plus hauling) costs approximately $27/ton, with an additional $10/ton for spreading (Fig. 2). To help offset the costs, the CDFA HSP provides incentives grants for farmers, and more funding may be available later this year. UC ANR Technical Service Providers Hope Zabronsky or Caddie Bergren are available to help growers with the application. And please don't hesitate to reach out to me if you would like more information on this trial or on the CDFA incentives programs.

Figure 2. Compost spreading at the San Joaquin County trial. Compost is not a small expense, but it may help improve soil functioning and alfalfa yield over the long-term.