Garden threats turned opportunities
Take a walk with new eyes: Most people walk through their garden with specific chores in mind. Those mental notes are handy for getting things done, but sometimes they can interfere with our ability to see the bigger picture. Try to see what works and what doesn't at the seasonal level, rather than noticing which plants need watering or weeding right now. Walking through your garden with these new eyes will help you identify three strengths and three threats within the landscape.
Three threats: Gardens and landscapes are not the tranquil sanctuaries they appear to be — they are battlegrounds. Plants, insects, pathogens, microbes, and many more are constantly battling one another for limited resources. Which three things cause the most trouble for your landscape? Is it slugs and snails? Aphids? Compacted soil? Is the soil too alkaline? By identifying the three biggest problems faced in your garden or landscape, you can focus your efforts specifically on them. Very often, correcting the biggest problems in a landscape improves overall plant health enough that they can handle the smaller problems on their own — and you can relax in the shade!
Three strengths: Every garden has its strengths. It doesn't matter what your garden's strengths are, but you cannot take advantage of them until they have been identified. Walk through your landscape and ask yourself which plants cause you the least amount of trouble. Which areas seem to have less pest or disease problems?
What types of weeds seem to turn up consistently? These conditions and plants can be used as indicators of what works best in your garden. After you pull weeds, ask yourself why those particular species are so successful in your yard. If most of those weeds have deep taproots (dandelions, mallow, prickly lettuce), try growing mustard, carrots, fennel, beets, and other root crops. Spreading weeds (wood sorrel, bindweed, spurge) can indicate the perfect location for mint or oregano. Use the natural characteristics of your garden's strengths and put them to work for you.
Identifying your landscape's strengths and weaknesses can help you stop fighting an uphill battle. Noticing what works in your landscape allows you to put effort where it will be most effective. This will help keep your plants healthier and give you more time to enjoy your summer.
by UC Master Gardener Kate Russell
Photo: Spotted spurge seedling. UC, by C. Elmore
This article first appeared in the July 15, 2017 issue of the South Valley Magazine.
First, you need to make it difficult and less desirable for larger mammals such as rats and rabbits to get to the garden. To deter rabbits, make sure the area is fenced, with the bottom of the fence at least 6 inches below ground. To discourage rats, remove all garbage or store it in a closed, animal-proof can.
Pick up and discard all fallen fruit or nuts. Clear away all hiding/nesting places such as low-growing branches and stacks of firewood; trim shrubs and foliage to at least a foot off the ground. Remove all sources of standing water: buckets, flower pots, bins, lids, and old tires. Keep your barbeque clean, as rats are attracted to leftover food and grease. If you are composting, don't add eggs, greasy food or meat and make sure you have a metal mesh barrier beneath to prevent them from coming up through the bottom.
My garden is fenced; I am growing only in raised beds and I have removed all standing water. As an avid animal lover, I don't wish harm on any living thing, not even a spider (most of which are extremely beneficial). However, last year, we lost nearly half of our tomatoes, lots of leafy greens and all but two or three of our persimmons to rats and rabbits. This spring, all of my sugar snap peas and most of my chard and kale were eaten down to the stems. And when something starts messing with your tomatoes it's time to take action!
We hired a trapping service, and it has been very effective so far. We have caught several rats, a handful of rabbits and even a few gophers and voles. There are several licensed services in the Bay Area that can legally trap and remove the animals from your property. My one remaining chard plant has now made a full recovery, there are hundreds of tomatoes on the vine that are just weeks away from ripening, and the persimmon tree (so far) is loaded with fruit.
Much smaller pests you may be seeing now include an array of aphids, beetles, worms, stink bugs and grasshoppers.
Aphids are tiny pear-shaped bugs that suck the sap from plant leaves, causing them to curl and drop. They leave honeydew, which promotes viral disease and sooty mold. Blasting your plants with a strong stream of water will wash away most of the aphids. Planting plants such as white alyssum, yarrow, and fennel will attract ladybugs, lacewings and other beneficial insects that devour aphids.
There are lots of beetles to look out for. Both the spotted and striped cucumber beetle have been prevalent this year. They do most of their damage before you even know they are there. Larvae attack the roots just as the plants are getting started. Adults will continue to wreak havoc, so hand-picking or vacuuming them off is important. They will attack not only cucumbers, but pumpkins, melons and all squash as well. Using row cover for seedings will help, but you need to remove it as soon as the flowers appear to allow the pollinators to do their job.
Caterpillars and worms can do lots of damage very quickly. You need to inspect the underside and inside of curled leaves thoroughly, as many blend in quite well with green leaves. Although it may be “yucky”, the best nontoxic pest control is to handpick and squish them.
Grasshoppers are one of the most difficult pests to control. If you see only a few, you can again handpick and discard them. Row covers can help. But if the population is high they can chew right through the cloth. Some gardeners have been successful in planting a row of tall grasses and other lush plants around the garden to divert their attention.
When all else fails, and you need to resort to a chemical solution, please bear in mind that the good bugs will be killed off alongside the bad ones. So use this as a last resort!
by UC Master Gardener Rebecca Jepsen
Photo from the San Jose Mercury News
This article first appeared in the July 22, 2018 print issue of the San Jose Mercury News.
If you have citrus trees, you likely have citrus mealybugs
Citrus mealybug description
All mealybugs are soft, flat, oval-shaped critters with segmented bodies. The mealybugs that attack Morgan Hill citrus are covered with a white wax that also creates spines (filaments) around the outer edge and the back end of the bug. Unless you use a hand lens you probably won't notice individuals, but mealybugs colonize areas creating white, fuzzy egg clusters that are easy to spot.
When mealybug eggs hatch the crawlers are pale yellow with red eyes, and distinct antennae. Crawlers are not born with their protective wax coating. They begin to excrete it soon after hatching. They are called crawlers because they crawl to a feeding site, where they will continue to develop (and damage fruit) for a month or two.
Citrus mealybug damage
Each female mealybug can lay hundreds of eggs, and there are usually two or three generations a year, so infestations can become a problem. As sapsuckers, citrus mealybugs pierce fruit, leaves, and young stems to get at the sap. They also feed on tender, new growth. As they feed mealybugs leave behind a trail of honeydew that attracts ants and creates the perfect growth medium for sooty mold. Citrus mealybug feeding near fruit stems also leads to fruit drop. This feeding also reduces fruit quality. Trees fail to thrive and are prone to infestation by disease and other pests. In addition to oranges, lemons, limes, and grapefruit, citrus mealybugs also have a taste for ornamental plants, such as tulips, coleus, cyclamen, begonias, and dahlias.
How to control citrus mealybugs
The first step to controlling citrus mealybugs is to monitor your trees, especially in spring and fall, for signs of ant trails, sooty mold, and egg clusters. Since ants will protect and farm the aphids for their honeydew, apply sticky barriers to tree trunks to block ants from protecting the aphids against natural predators. Those natural predators are your trees' best defense against citrus mealybugs. Lady beetles, lacewings and hoverflies will devour these pests so avoid using broad-spectrum pesticides. For extreme infestations, you can buy an introduced predator called the mealybug destroyer (Cryptolaemus montrouzieri). Insecticides are not recommended. Diatomaceous earth and insecticidal soaps can also be used.
Mealybugs prefer dusty conditions so hosing trees off can make them less appealing to citrus mealybugs.
by UC Master Gardener Kate Russell
This article first appeared in the March 23, 2018 issue of the South Valley Magazine.
Cabbage aphids wreak havoc in the garden
Cabbage aphids (Brevicoryne brassicae) can wipe out a cabbage crop before it ever gets started. Native to Europe, this pest of cole crops is now found throughout the United States.
Like other aphids, cabbage aphids are small, teardrop-shaped, sap-sucking pests that can reproduce at an alarming rate. While soft-bodied cabbage aphids are actually grayish-green, they look powdery blue to grayish-white because of a waxy covering. Cabbage aphids are not difficult to see because they live in dense colonies that can cover stems, new leaves, and entire plants practically overnight. In our moderate climate, these pests produce live offspring year-round.
Cabbage aphids have an amazing defense mechanism. They produce an enzyme in their head and throat muscles which gets combined with defensive chemicals (glucosinolates) from their host plants to create an explosive chemical reaction. This reaction produces mustard oil. Unfortunately, this “walking mustard oil bomb” defense is particularly effective against ladybug larva.
Cabbage aphids feed on the youngest, most tender parts of new cabbage, broccoli, Brussels sprouts, kale, and cauliflower. These pests also eat the innermost parts of cabbage and Brussels sprouts heads. Large colonies can stunt or even kill young plants. Heavy aphid feeding causes leaves to curl up, providing the pests with a protective cover.
Prevention is key to cabbage aphid control. Row covers are an excellent way to protect young crops while they are getting established. Once aphids are seen you can often use a strong spray from the garden hose to dislodge them. If that doesn't work, insecticidal soaps can provide some control. Since some insecticidal soaps may be phytotoxic (meaning sunlight causes them to burn the plant), it is a good idea to apply them on a foggy day, especially for cabbage and Brussels sprouts.
Another way to make life more difficult for cabbage aphids is to remove any weeds in the mustard family from your property. Cabbage aphids hide out in the mustard and then return to your garden plants. Pesticides can be used as a last-ditch effort, but aphids are developing resistance to these chemicals—a potentially dangerous spiral.
Another problem with using pesticides against cabbage aphids is that those same chemicals also kill beneficial, predatory insects, such as lady beetles, parasitic wasps and syrphid flies (hoverflies). These helpful insects are natural predators of caterpillars, imported cabbage worms, diamondback moths, loopers and armyworms, which can cause other problems for your cole crops.
Monitor your plants every couple of days and be on the lookout for cabbage aphids!
by UC Master Gardener Kate Russell
Photo: South Valley Magazine
This article first appeared in the February 9, 2018 issue of the South Valley Magazine.
The chemistry behind oxalic acid
As an acid, oxalic acid is corrosive. It is used as an industrial bleaching agent and heavy-duty cleaning product. Apparently, it works especially well on removing rust. Oxalic acid is also classified as nephrotoxin, which means it can damage your kidneys. Oxalic acid, in the form of calcium oxalate, is the most common ingredient of kidney and urinary tract stones. Oxalic acid can also cause joint pain. At high concentrations, oxalic acid really is deadly. According to the National Institutes of Health, lethal doses range from 15 to 30 mg, though an oral dose of 5 mg has been fatal.
In each of these cases, it is the amount of oxalic acid being ingested that is the problem. The levels found in many foods are too low to cause problems. Bottom line, a 150-pound person would need to eat approximately 12 pounds of rhubarb leaves for it to be dangerous. And spinach leaves contain more oxalic acid than rhubarb leaves. That's why your teeth may feel funny after eating spinach. It's oxalic acid crystals binding with any nearby calcium to create calcium oxalate crystals. These crystals stick to your teeth for several minutes to an hour.
Oxalic acid in nature
Oxalic acid is found in a surprising number of food plants that we eat every day. The trick is in the concentration. In fact, oxalates can be toxic to plants, too, but plants bind those oxalates up in crystals that they then use as tiny spears to defend themselves against herbivores. These specialized cells are called idioblasts. Oxalic acid is formed when plants burn sugars and carbohydrates as fuel.
Oxalates are also used to balance calcium levels, within the plant, by binding to calcium molecules. This is why some people say eating high levels of oxalic acid can interfere with healthy bones and teeth, but, again, you would have to eat an awful lot—over a long period of time—to cause any real problems. By the way, our bodies produce oxalic acid out of Vitamin C, on purpose. Also, cooking plants that contain oxalic acid has not been shown to reduce oxalate levels.
Armed with this information, I went out to my rhubarb plant and broke off a young leaf and ate it. The flavor was actually pretty nice, something akin to spinach, but lighter. And I lived to tell about it.
by UC Master Gardener Kate Russell
Photo: South Valley Magazine
This article first appeared in the January 5, 2018 issue of the South Valley Magazine.