Spring means new shoots and growth and flowers….and bugs, and fungus, and questions galore. So it's Q & A time in the garden! Control measures may be available, but oftentimes a little patience will reward you as nature provides a remedy.
Aphids seem to come out of nowhere. Pregnant winged females land and pop out pregnant female babies at the rate of 50 - 100 per day. On roses they are right up on the buds, fat and foolish, so they can be blasted off with water or sprayed with pyrethrins, soap, or oil. Leatherwing beetles and the larvae of lacewings, hoverflies, and ladybugs often give reasonable control,. so don't be too quick to spray.
The black aphids on trees are tougher, as they cleverly cluster under the leaves. An oil spray will smother them, but it's hard to get the spray under the leaves. Wait and see, though; if any of them appear listless and bloated, and have turned tan, they have been parasitized by a very common natural predator and the problem will take care of itself.
The Asian woolly hackberry aphid is now fully established in all parts of town. For an update on the life cycle and management, visit our website at www.redwoodbarn.com, and click on Pest Notes. The sticky stuff is almost pure sugar solution, so it is soluble and washes off of surfaces, and the trees aren't being weakened by the pest. But it is incredibly annoying, to the point that people are contemplating removing the trees.
Before you cut down the tree, consider the value it adds to your property (and if it's your street tree, don't even think about it! Send all comments to Bob Dunning…). Even with the annoying sticky drip, a mature hackberry adds thousands of dollars in value to your property, not to mention providing summer shade. Early reports from those who are using the systemic control products (available at Davis Ace and Redwood Barn) have been very favorable. The application rates are based on the circumference of the trunk: one ounce per inch for the drench, one cartridge per four inches for the injections. Be sure to read the label and ask for directions about how to apply them.
Take a flashlight out at night, which is when the pests are feeding….big holes are from snails and slugs (the slimy trail is a clue), and little holes are from earwigs. Snails and slugs are easily controlled with Sluggo, an iron phosphate compound that breaks down into fertilizer.
Earwigs emerge from their dens in April, and increase through May until they disperse. Although they feed on other insects and debris, they also nibble on young seedlings, rose petals, hollyhock leaves, and certain other plants. Most years their populations are not excessive, but we do have localized outbreaks when they seem to be everywhere. Carbaryl (Sevin) baits are available, but they're combined with metaldehyde so are unsuitable around edible plants (plus, they don't seem to be real effective anyway). Trap earwigs with oil. My favorite trap is a milk carton with an inch or so of water and a glug of a fragrant oil (corn, peanut, or olive), tipped on its side with the spout open and upward. Curious earwigs crawl up, slip in, and drown. Curious relatives gather to gawk… and fall in.
What are the yellow spots on my rose leaves?
Small yellow spots on the upper sides of the leaves, with small orange pustules on the lower sides, are rust. This common fungus is difficult to control, but just picking off the affected leaves can make a big difference. Avoid watering with an upward spray such as a sprinkler; drip, bubblers, or overhead shower-type watering is ok. The hard pruning we do in the winter helps remove the overwintering spores.
Larger yellow spots are usually downy mildew or black spot (both may be present). Downy mildew, in particular, causes the leaves to yellow and drop. In the rainy April of 2003 roses virtually defoliated. The good news is a dry windy spell will stop the spread of this disease and most others. Rake up the fallen leaves, trim back the plants if necessary, and give a feeding with a slow-acting fertilizer to help the bush replace the lost foliage.
How about the white powder on my roses?
That is powdery mildew. The leaves don't drop, so the plant isn't actually harmed by it, but it is unsightly.
Some varieties are very prone to it; others range from moderately susceptible to immune. So selecting your rose carefully in the first place can be a big help. Hosing the plants off early in the day not only dislodge aphids but also blasts off mildew spores.
What are the dead branches on my apple tree from?
Rapid blackening of new growth on apples -- and pears, and related ornamentals such as crabapples, quince, and Pyracantha,-- is caused by the bacterial disease fireblight. This fast-spreader can kill the tree if it goes unchecked, but fortunately it has a narrow temperature range: 55 - 80F. This year the nights have been too cool, and the few warm spells too hot, for it to make much progress. Prune it out as soon as you see it, and monitor those trees closely when we're in that temperature range. In bad years whole branches or trees may be killed if you don't remove the blight quickly.
Isn't there anything to spray for these diseases?
The fungicide selection available to home gardeners has dwindled as manufacturers have discontinued many products. But new, safer products are replacing them.
Our local company AgraQuest has one which is now available to home gardeners. Serenade is a bio-agricultural fungicide derived from a Bacillus, a beneficial bacteria closely related to the species which have been used against caterpillars and mosquitoes. This one kills quite a range of harmful fungi and bacteria, including all of those mentioned. Available only in a ready-to-use form at this time, it should be available to homeowners in an economical concentrated version next year.
What's eating my citrus leaves, fruit, and bark?
Holes in the leaves are from snails. They are the major pest of citrus. Fortunately, they're easy to control: put a band of copper tape around the trunk. Copper gives snails a shock, and they won't crawl over it.
Other damage can be more mysterious. This morning there was a neat pile of peeled kumquat fruit at the base of my tree. Tree rats (and possums) love citrus fruit almost as much as we do. But apparently my visiting rat doesn't like the tart flesh of the kumquat--just the sweet peel. Oranges may have a neat hole in the peel, and all the flesh missing. Lemons usually have a few bite marks. Rats and possums will sometimes strip the bark off of citrus as well. The only controls for animal pests are poisons (please be careful!), traps, or exclusion with poultry wire. Or cats, but mine have been remarkably ineffective.
Why do you keep telling me it's too early to plant my peppers and eggplants outside?
Because they will sulk all season if they go into cold soil. Go sit on the ground early in the morning. Comfortable? No! Neither are these veggies! Night temperatures should be consistently above 55F (preferably 60F!) before these go in the ground. We're still in the 40's at night! Tomatoes will sit and wait for warmer temperatures, though they may turn purplish. But the real heat lovers--and this includes okra--will never catch up.
The good news is it WILL get warm, and there is plenty of time to get these planted. And the dry warm weather will also put a stop to all of the pests and diseases mentioned above. In the garden patience is a virtue, and procrastination is often rewarded!
© 2008 Don Shor, Redwood Barn Nursery, Inc., 1607 Fifth Street, Davis, Ca 95616
www.redwoodbarn.com
Feel free to copy and distribute this article with attribution to this author.
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