The drone of orchard sprayers at sunrise reminded me that there is a downside to the unseasonably cool, damp weather we’ve been having.
Fungus diseases require high moisture to inoculate and establish. Twice in the past month we’ve had two- to three-day intervals of overcast with light sprinkles.
Expect disease problems, ranging from powdery mildew on crapemyrtle and cucumber to blight on sycamores, to show up in about seven to 10 days. I imagine wine grape growers are worried. And in your garden, soft-bodied insects such as aphids and whiteflies may show population increases due to the mild weather.
Usually by summertime, beneficial insects that control garden pests have increased, keeping the pest populations at acceptable levels. High temperatures and low humidity slow the reproductive rate of the aphid. Expect a little surge in those populations. A return to hot, dry weather will ordinarily put a stop to the spread of any disease or pest outbreak.
Which brings us to this week’s related question about summer pests: West Nile spraying.
They’re spraying around Davis for mosquitoes due to West Nile virus. What will that do to my garden?
From a news release reported in The Enterprise Aug. 5: “… the Sacramento-Yolo Mosquito & Vector Control District has scheduled aerial spraying of a low-toxicity insecticide over Davis and Woodland this week. The insecticide Trumpet will be dispersed at ultra-low volumes over the cities.”
Spraying was set to occur Wednesday and Thursday in the evening, weather permitting.
I have anecdotal reports from gardeners around Sacramento where spraying has occurred about sudden increases in aphid and whitefly populations shortly afterwards. This makes sense. The material being applied doesn’t kill mosquitoes selectively. We would expect some harm to populations of beneficial insects, particularly small ones such as the parasitic wasps that help keep aphids in check.
From studies I have seen, larger insects such as dragonflies, honeybees, spiders and butterflies are not affected. The dosage is low, and the spraying is done at night when those aren’t active.
Doesn’t the spray kill aphids, too?
Probably, at least some of them. But their reproductive rate means their populations will rebound faster. Good news: The beneficial insects will catch up and restore the equilibrium within a couple of weeks.
Should I spray the aphids and whiteflies?
That likely would kill the good guys too, and keep them from coming back. Manage aphid and whitefly problems by vigorously rinsing with water. Blast the plant, especially on the undersides of the leaves, early each day for three to four mornings in a row. You’ll wash off young aphids, eggs and larvae of whiteflies, and spider mites. Beneficial insects won’t be harmed.
But my garden is organic.
Unfortunately, the spray material they are using is not organic. But according to the label, it washes off.
Other bugs in the summer garden:
What is this giant bee?!? It’s about two inches long, fuzzy, golden!
This giant, fuzzy, charming, friendly creature is the male of the carpenter bee. Stingless, harmless and short-lived, it always startles people when they encounter it during early summer. Carpenter bees are pretty good pollinators, attracted to a range of flowers but especially to tubular ones such as penstemons and salvias.
There are caterpillars eating my passionflower vine!
Last month’s column was about drawing beneficial pollinators to the garden. One way to do that is to plant larval food sources. In the case of the Gulf fritillary butterfly, the larvae feed exclusively on Passiflora species: passionflower vines. So if you want the butterflies, you need to tolerate the damage from the caterpillars.
Caterpillars of many moth and butterfly species can do a lot of damage in a short time. They need to eat huge amounts of leaf material as they grow quickly before they pupate.
The good news is that this is a fairly short stage, and most plants can quickly outgrow the leaf damage, so control measures aren’t really warranted. By the time you notice the defoliation, they’re nearly done. And birds can do a pretty good job of reducing the population numbers.
If the problem is severe, you can spray with the organic products that contain BT. They kill caterpillars only, and work best when the caterpillars are still young.
Do you have a spray for spiders? They’re all over the place. Do they do any good in the garden?
Don’t spray for spiders. A good spider population is a sign of a healthy garden. They are beneficial in the sense that they eat pest insects. They are general feeders, so they also eat beneficial insects, and each other. The common spiders that you see in your garden are not aggressive or harmful.
Orb-weavers spin the beautiful webs that stretch across garden paths. Just take a stick and relocate the corner of the web to move them out of the way. Note how she scrambles in the other direction as you do so.
Crab spiders lie in wait in flowers to catch unsuspecting flying insects. Shake off flowers before you bring them into the house.
These are just a couple of the types of spiders helping to maintain the balance of nature in your garden.
We do have black widow spiders here, and they are well-known for their venomous bite. They are surprisingly common, yet the bites are rare. That is because they like dark places, don’t like to be disturbed, and will typically scramble further into the darkness if you expose them to sunlight.
Wear gloves when moving firewood, cleaning up debris piles or rummaging deep into garden sheds. Sprays are really not effective for spiders. Just know their habitat and cover your skin when you are invading their spaces.
Contrary to popular belief and current Internet memes, we do not have brown recluse spiders here.
I found these giant bugs on my pomegranate tree. Do they do any harm?
Leaf-footed bugs (Leptoglossus) seem to be in high numbers this year. Their population fluctuates, so this may be related to drought, late-spring rains or winter weather. The name refers to flat leaf-like protrusions on the hind legs, or what entomologists call “foliaceous hind tibiae.” It is considered a minor pest of nut and fruit crops; gardeners mostly find them on tomatoes and pomegranates.
These are among the bugs that cause misshapen and blemished peaches, nectarines and tomatoes from their early-season feeding as the fruit is developing. The fruit is usable. Damage to mature tomatoes is minimal (you probably won’t even notice it). Their strong mouthparts can penetrate pomegranate skin and suck the juices of a few of the little arils, but most of the fruit is unaffected.
Management involves removing overwintering weeds (especially thistles) and cover crops by mowing before fruit sets on your nearby trees. They overwinter inside unpicked pomegranates that hang on the tree or rot on the ground during winter. Maintaining a clean orchard floor is a basic principle of disease and pest management in fruit orchards, and a good idea for home gardeners as well. The old reliable pick-and-stomp technique also works.
A quick change of subject: new plants!
In our industry we are bombarded with promotions of exciting “new” varieties of flowers. We get a little jaded: how many petunia hybrids do we really need? So when something genuinely new comes along, it creates a buzz among gardeners and plant professionals.
Plant breeders crossed Digitalis (foxglove) with a related shrub named Isoplexis. This yielded Digi-plexis, a bushy plant with foxglove-like spikes of flowers over a very long season, May until frost by most accounts. From the shrub parent we get basal branching and a nice full habit. The color is unique, a sort of coppery-pink.
Where to plant them? Our best guess for the valley is partial shade or morning sun. Not fussy as to soil. Regular watering. A new perennial for Davis gardens!
— Don Shor and his family have owned the Redwood Barn Nursery since 1981. He can be reached at [email protected] Archived articles are available on The Enterprise website, and they are always available (all the way back to 1999) on its business website, www.redwoodbarn.com