- (Focus Area) Environment
- Author: Kathy Keatley Garvey
It's Friday Fly Day, when folks post images of flies.
Flies seem to the entomological equivalent of Rodney Dangerfield's "I-don't-get-no-respect" quote.
So how about a black syrphid fly, a Mexican cactus fly, Copestylum mexicanum, nectaring on a Mexican sunflower, Tithonia rotundifolia?
The genus Copestylum includes more than 350 species in the new world, according to Martin Hauser, senior insect biosystematist with the Plant Pest Diagnostics Branch of the California Department of Food and Agriculture (CDFA).
The female Mexican cactus fly lays its eggs in rotting or dying cactus tissue.
This fly, about 3/4 of an inch long, is a delight to see in a patch of Mexican sunflowers mostly frequented by honey bees and Gulf Fritillaries. It's big. It's bold. And it's beautiful.
Happy Friday Fly Day! Respectfully...
- Author: Kathy Keatley Garvey
In your childhood, somebody probably gave you a jack-in-the-box toy, a music box that you crank up, and then the lid springs opens and out pops a wildly dressed clown, startling you and everyone around you.
A praying mantis sighting is something like that, but without the music box. You're walking in the garden and suddenly you notice that the Mexican sunflower, Tithonia rotundifola, appears to have an extra petal.
You look closer and you see a triangular head with bulging eyes. And a spiked foreleg that looks as if it's extending a hand in (fake) friendship. It's a praying mantis and it's staring right at you.
Such was the case recently when a female praying mantis, Mantis religiosa, popped up between the petals.
Jackie-in-the-box!
"Nice to meet ya, m'dear," she seemed to be saying. "Too bad you're not a bee."
- Author: Kathy Keatley Garvey
It's beginning to look a lot like...Halloween.
If you haven't noticed, stores are gearing up for Halloween with assorted ghosts, goblins and ghouls for you.
We remember Halloween 2023 when a female migratory monarch fluttered into our pollinator garden. She checked out the milkweed (we had several native and one non-native species) and chose to sip nectar on the tropical milkweed, Asclepias curassavica, a non-native.
We managed to capture several images of her around 5:30 p.m. before she left on her journey to overwinter in coastal California.
The Center for Biological Diversity, headquartered in Tucson, says on its website: "Across their range, monarchs are threatened by pesticides, climate change, ongoing suburban sprawl, and fragmented and poisoned habitats as they navigate their way across the continent. They need a helping hand from the government, businesses and concerned individuals."
Threats? To that we'd add a minor threat: such predators as birds, spiders and mantises.
Monarchs in western North America overwinter in coastal California (roosting in eucalyptus, Monterey pines, and Monterey cypresses), while those in eastern North America "have a second home in the Sierra Madre Mountains of Mexico" (roosting in oyamel fir forests), as noted by the U.S. Forest Service.
"Researchers are still investigating what directional aids monarchs use to find their overwintering location," the U.S. Forest Service says. "It appears to be a combination of directional aids such as the magnetic pull of the earth and the position of the sun among others, not one in particular."
We're glad to see that the raging controversy over native vs. non-native milkweed is subsiding a bit, as the more crucial threats are pesticides, habitat loss, and climate change. After all, tropical milkweed, a native of Mexico, has been in California for more than 100 years. And longer than that when you consider that California was once part of Mexico. A. curassavica is also native to Central America (including Belize, Costa Rica, El Salvador, Guatemala, Honduras, Nicaragua, and Panama) and South America (including Colombia, Ecuador, Peru, and Venezuela), according to Johnny Butterflyseed.
- Author: Kathy Keatley Garvey
So, here you are, a newly eclosed Western tiger swallowtail, Papilio rutulus, eager to sip some nectar from a Mexican sunflower, Tithonia rotundifola, in a Vacaville garden.
It's a warm, windless day, and you're anxious to score, score, score.
You touch down on a Tithonia, but something whizzes by your tails.
Whoa! What was that?
You're startled, alarmed, and irritated. It's a territorial male long-horned bee, probably a Melissodes agilis. He aims to dislodge you from your blossom in his attempt to save the nectar for his would-be girlfriends.
You teeter, then totter, then take off. You touch down on another Tithonia.
Hey! Bee brain! Quit targeting me? Go away!
You head for another blossom, determined to grab a least "a little" nectar.
Stop it! Leave me alone! Go take a vacation!
But the bee isn't about to take a vacation. And he won't allow your "staycation."
Spoiler alert: The butterfly admits defeat and departs the flower garden, exasperated but with tails intact. The bee emerges victorious, its real estate intact.
Score: Bee, 3, Butterfly, 0.
The turf battle is over for today. Tomorrow? That's another day and another battle.
- Author: Michael D Cahn
Introduction
Traditional winter cereal cover crops planted in the Salinas valley have many potential benefits including, scavenging nitrate in the soil profile, increasing organic matter in the soil, and protecting the soil from erosion during storm events. However, when grown for 3 to 4 months during the late fall and winter, cereal rye, triticale, or barley can accumulate 5 to 6 tons of dry matter biomass that must be incorporated into the soil before planting a spring vegetable crop. Tilling in a high amount of cover crop biomass can be disruptive to spring planting schedules. Consequently, only a small fraction of the vegetable ground in the Salinas valley is cover cropped each year.
Previous studies demonstrated alternative strategies can limit the biomass growth of these cereal cover crop species so that they can more easily be tilled into the soil, and therefore less disruptive to spring planting schedules. After fall land preparation, the cereal cover crops are seeded into listed beds and/or in the furrow bottoms. After they become established they can reduce runoff and protect the soil from erosion during early winter storm events. Before the cover crops grow too big, they are terminated with an herbicide to limit the amount of above ground biomass that needs to be incorporated in the spring. For organic systems, planting a mustard cover crop on listed beds or furrows which can be terminated mechanically by mowing is another strategy to limit biomass. A good target for these low biomass cover crops is between 0.5 to 1 ton of dry matter per acre by the date of termination. Once terminated, the biomass begins to decompose. However, the residue on the surface continues to protect the soil from erosion and can significantly increase infiltration from rain events. This helps to leach accumulated salts in the soil as well as recharge groundwater aquifers. The remaining decomposed residue can easily be incorporated into the soil during bed preparation in the spring.
One risk of this low biomass approach is accessing fields during the winter to terminate the cover crop. If soil conditions are too wet or if there is not enough available labor, it may be difficult to fit in a spray application or to run a flail mower. This termination step also increases the cost of managing the cover crop. A possible solution is to use species that grow slowly during the winter when temperatures are cold. Sudangrass and sorghum-sudangrass hybrid are warm season adapted species that could be used in this low biomass approach to managing winter cover crops.
Field trial with warm season adapted cover crop species
A field trial was conducted with sudangrass and sorghum-sudangrass in the 2023-2024 winter to evaluate biomass growth, and the effect on storm water runoff and soil erosion compared to bare-fallow plots. The site was located on an Arroyo Seco gravelly loam soil with a slope of more than 5%. Plots measuring 1050 ft in length by four 40-inch wide peaked beds were planted with either sudangrass, sorghum sudangrass hybrid, or left bare fallow. Treatments were replicated 4 times. The cover crops were seeded at 60 to 80 lbs/acre on October 4th and were subsequently sprinkle-irrigated several times. Total water applied for establishment was 2.6 inches. One application of the herbicide Bromoxnil (Maestro) was applied about 45 days after planting to kill emerged broadleaf weeds.
Results
Above ground biomass, N uptake, and carbon accumulation
Both cover crops had limited biomass growth, accumulating only 0.35 to 0.5 tons/acre of dry matter by early January and less than 1 ton/acre by mid March (Table 1). Growth was set back by cold conditions that occurred from mid November through early January, occasionally reaching freezing temperatures which caused damage to leaves (Fig. 1). However, the freezing temperatures lasted only a few hours and were not severe enough to kill the cover crops (Fig. 2). By March 13th the cover crops had taken up 45 to 55 lbs N/acre and had a carbon to nitrogen ratio of 15. The C:N ratio of 15 would suggest that after soil incorporation the residue would decompose rather quickly and release N for the following vegetable crop.
Runoff, rainfall infiltration, and control of soil erosion
Total rainfall measured at the trial site was 10.2 inches for the winter season. The most intense period of rainfall occurred in late January and early February which resulted in several runoff events (Fig. 3). During this period about 50% of the rainfall in the bare fallow plots was lost as runoff compared to 15% lost as runoff in the cover crop plots (Fig.4). Over the entire winter season, runoff was reduced by an average of 70% under the cover cropped plots compared to the bare fallow plots, and significantly more rainfall was infiltrated into the ground in the cover cropped plots. In addition, suspended sediment concentration was 90% and 77% less in the sudangrass and sorghum-sudangrass cover crop plots, respectively, compared to the bare plots. Turbidity, total P, and total N concentration in the runoff were also reduced under the cover crop plots compared to the bare fallow plots (Table 2).
Seasonal soil erosion losses could be calculated based on the volume of the runoff and sediment concentration in the runoff. The total loss of sediment averaged more than 3500 lbs per acre in the bare fallow plots during the winter, while erosion losses were reduced by 96% to 98% in the sorghum-sudangrass and sudangrass plots (Fig. 5). Total N losses were reduced by 83% to 86% in the cover crop plots compared to the fallow plots, and total P losses were reduce by 81% to 85% in the cover cropped plots compared to the bare fallow plots.
Conclusions
The use of warm season species such as sudangrass and sorghum-sudangrass hybrids as winter cover crops provides several advantages compared to planting cereal cover crops. The biomass growth through the winter is self-limiting due to the cold conditions that typically occur in the Salinas Valley. Because the final biomass would likely be less than 1 ton per acre, these species can be planted on listed beds in the fall rather than on flat ground. This means that in the spring, the remaining cover crop can be lillistoned into the peaked beds a few weeks before final bedshaping and planting. Cover crops planted on flat ground and have high amounts of biomass usually require many tillage passes to prepare ground for planting. Despite, having less biomass than traditional winter cereal species, sudangrass and sorghum-sudangrass hybrid cover crops provided excellent erosion control compared to leaving the ground bare, and increased infiltration of rainfall during storm events. Also these species may be able to scavenge significant amounts of nitrogen from the soil which can limit nitrate leaching during the winter months.
On the east-side of the Salinas Valley groundwater levels have been in the decline for several decades. Infiltrating as much rainfall as possible during the winter using strategies such as low biomass cover crops could potentially help recharge the aquifer in this region. We plan to conduct a second year of field trials with these warm season species to continue evaluating this approach to managing winter cover crops in vegetable systems.
Acknowledgments
This project was funded by the California Leafy Greens Research Board.