1. Is there a simple way to tell how much water my lawn needs? We just moved to a new house and the lawn is showing signs of needing water. We water daily for 4 minutes.
Four minutes per day is likely too short and too frequent a schedule to allow lawns to dry out a bit between watering or for water to penetrate deeply. Daily watering promotes shallow root growth, making the turf very susceptible to insect damage, fungal growth, and disease.
The website http://www.ipm.ucdavis.edu/TOOLS/TURF/MAINTAIN/output.html shows an easy way to check water needs with a schedule for each county. (Yolo County falls into two regions .) A rule of thumb for the hot months of July, August and September is 1.5 to 2 inches of water per week in Yolo County.
Now, evaluate your sprinklers by laying out containers such as coffee mugs, tuna cans, or cat food cans evenly on your lawn. By knowing the output of your sprinklers, you can adjust the controller of your sprinklers for the desired weekly output. If you see water streaming down the sidewalk from too much water during a single application, adjust the time period and add a second cycle three to four hours later, allowing the water from the first cycle to seep into the soil. It is best to water during the coolest time of the day, usually 4 to 10 a.m. Earlier is better as this reduces the loss of water due to evaporation.
The can test is also a good way to see what your sprinklers are missing, and what sprinkler heads need to be replaced. For ease of replacement, take pictures of the heads or bring one to the store. Finally, even though we are starting our hot season, when the days become shorter and the temperatures cool, adjust the timing on your sprinklers accordingly. Put a reminder on your calendar sometime around October or November to readjust the time cycle.
2. Tomato spotted wilt virus: Is it different than other viruses? Are disease-resistant strains safe from it? What can I do if my tomato has it?
Tomato spotted wilt virus (TSWV) is different than other viruses due to the size of its spherical particles. It is spread by insects called thrips from plant to plant and is not present in the soil. This virus has been a bigger problem in the American South and Northeast than here, probably due to its origin in more tropical climates, but it still occurs. Contamination in seedlings usually occurs in when thrips travel between seedlings in greenhouses that grow ornamental plants and susceptible vegetables like eggplants and tomatoes.
Keeping your garden free of plants that serve as hosts to thrips can help avoid infection with TSWV. These would commonly include blue morning glories, lambs quarters, bindweed and purslane, among others. Insecticidal soaps can help control thrips but not necessarily enough to make a significant difference. (See UC IPM.) There are disease-resistant varieties available such as the Amelia and some Roma tomatoes, but they are rather difficult to find in our area. You can research seed companies for these and other resistant strains.
If your tomato has this disease at seedling stage, pull and dispose of the plant. If it occurs on mature plants, the fruit is still edible although not attractive. On older plants, try insecticidal soap.
3. Why is the lemon tree in our yard dropping all its leaves? This is in an area of the yard with black plastic over soil where we water daily.
A common problem among citrus trees is leaf drop. Any number of reasons can apply. However, great fluctuations in temperature can cause the leaves to drop and this may be your problem. Temperatures have certainly fluctuated this spring from very warm to cool to rain and back again.
Be your own garden detective. Do the leaves wilt, turn yellow or brown, curl or are distorted? How old is the tree? Has anything changed in regards to the tree (more frequent watering, other plants added recently around the tree)?
Trees prefer deep watering on an as-needed basis. Watering every day may not allow the water to soak deep into the soil and reach the full depth of the roots. It may also signal the opposite, too much water. The black plastic may not be allowing the water to soak deep into the soil but rather cause water to run off and can heat up the soil. A better solution for weed control, water conservation and the overall health of your garden is to use compost and top dress with mulch.
Scrape the bark to see if the branches are still green. If so, there is still hope for the tree.
Public Workshops by Master Gardeners Saturday, June 15:
9:30 a.m. — Master Gardener Merle Clarke will lead a free tour of the Davis Community Garden located at 1825 Fifth St. in Davis.
10 a.m. to noon — Master Gardener Erin McDermand will teach a “Basic Integrated Pest Management Class for Home Gardeners” at the Arthur Branch of the Yolo County Library located at 1212 Merkeley Ave. in West Sacramento.
Send questions, addressed to the Garden Doctor, by email to firstname.lastname@example.org, voice mail to 530-666-8737, or regular mail to UCCE Master Gardeners, 70 Cottonwood, Woodland, CA 95695. Be sure to include your contact information, because any questions not answered in the Garden Doctor column will be answered with a phone call or email to you. You can request the Yolo Gardener newsletter delivered by email and learn more about the Master Gardener program in Yolo County at http://ceyolo.ucdavis.edu/Gardening_and_Master_Gardening.