Questions from area gardeners

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By David Graper

SDSU Extension Horticulture Specialist

Damaged Norfolk Island pine

Q I put my 2’ tall Norfolk Island pine outside for the summer. An animal (probably a squirrel) ate most of the branches off at the main ‘trunk’. Will the branches grow back with time? Thank you for your help.

A Norfolk pines do have a limited ability to develop new shoots from the ends of damaged branches but if the branches were chewed off from the main “trunk”, I doubt that any will grow back. If the main stem tip is still intact, new growth and branches may develop from that point. However, if your plant is just 2′ tall, I think it may be better to just start over with a new plant. They are not that expensive and usually readily available as we near the Christmas season again later this fall and early winter.

I understand the desire to move houseplants outdoors for the summer to give them a chance to get better light and grow faster for a few months. But, often they suffer more negative effects from the move than if they had just been kept inside the home. Excessive sun exposure, excess heat and water stress, storm damage, insect damage, frost damage in the spring or fall and damage from animals as in this case are all too common. If a plant is doing well indoors, it is often best to let it there and not move it outside during the summer.

Grass sample

Q Client stopped in with this sample (see photo). What is this? How do I get rid of it in my new grass? Ground was tilled in April and planted with a blue grass mix in early May 2018.

A This appears to be crabgrass, a common warm season weedy grass, that is particularly a problem in newly seeded lawns that were planted in the spring. The challenge is that when a cool season grass, like Kentucky blue grass, is planted in the spring, it takes about 3 weeks for it to germinate then another 4 -6 weeks for it to really get established and become competitive with other plants like the crabgrass.

You can try using a post-emergent crabgrass killer, usually containing Quinclorac as the active ingredient, often in a mix with some broadleaf herbicides for use on lawns. This will be most effective when it is applied before the crabgrass starts to sprawl out along the ground (see first picture) and begin to produce it flower/seed heads. (see second picture). Once it reaches these more advanced stages of growth it is very difficult to control. Raising the mowing height to 3″ or more will help the new planted grass to be more competitive as well. Next spring, about the time lilacs are seen blooming in your area I would highly recommend that you apply a crabgrass preventer to your lawn because you will very likely have a good crop of seed from this year’s crabgrass plant. An individual plant can produce about 100,000 seeds! Crabgrass preventers are usually found as part of a fertilizer blend in stores in the spring of the year, often labeled weed and feed. But be sure it says is it for crabgrass prevention, not control of broadleaf weeds.

Plant identification

Q I planted a mix of wildflowers from seed this spring and now I am having a hard time identifying them. I am wondering what they are and whether they are perennials and if so how best to plant them in the ground for next year. I have included photos each of three pots I have grown. Thank you.

A The first one with the yellow flowers is a type of coreopsis, may or may not be hardy here, it is hard to tell without more information. Many are annuals and some only hardy to Zone 5.

The large green plant in the white pot appears to be a type of amaranth. These are usually only annuals for us.

The last one with the red flowers is a zinnia, also an annual.

Sorry, but I don’t think you have anything there that will be worth transplanting for next year.

Hydrangea not blooming

Q Three springs ago I bought two endless summer hydrangea bushes and planted them. They produced blooms the first year (had them already when the plant was purchased). The second year, they bloomed but less so, and this year no blooms at all. I did some soil testing in the area last fall and there were little to no nutrients. I fertilized last year and again this spring. Not only did I not get blooms this year, the plant did not green up or grow. The plantings are on the south side of our house but near a tree that shades the area during parts of the day. The soil there is also more on the clay-like type, so perhaps it doesn’t drain the way it should. Just wondering if there are other things I should consider. I did move one of the plants to a large pot a couple weeks ago and placed it on the east side of the house, away from any tree shade. I am hoping I might revive it. Any other thoughts or suggestions are appreciated. Thank you.

A Unfortunately, the ‘Endless Summer’ Hydrangea have not turned out to be very good plants for us this far north. They generally bloom on last year’s wood. So, you have to have stems that grew last year survive the winter to produce the flower heads. If the majority of the stems die back over the winter, which is fairly common here, you might only get a few blooms later in the summer. That is because this plant can have limited blooms develop on new wood as well.

There are several other cultivars of hydrangeas, particular of H. paniculata, that are hardier and much more reliable bloomers. You might give those a try. Having your soil tested was a good idea but I do not think that low nutrient level was the cause in this case. Hydrangeas do not normally need a lot of nutrients to grow and bloom. they also prefer a semi-shaded location because they will suffer from heat and drought stress during the summer months.

White flying bugs on my tomatoes

Q I was out in my garden, beginning to harvest tomatoes, when I noticed small white flying bugs that would fly around as I was trying to get at the ripe tomatoes. I have never seen these on my tomatoes before. (See photo.) What are they? Are they hurting my plants? Should I be spraying something to get rid of them?

A What you are describing are whiteflies. These are not true flies. They actually look more like very tiny white moths, but they are not a moth either. They are actually closely related to aphids. They feed by sucking plant sap from the leaves and produce honeydew, like aphids and soft scales. They tend to hide on the underside of leaves so may be hard to see, unless you disturb the plant, causing them to fly up and around plant. Ordinarily they are a problem that shows up in the greenhouse but occasionally they can be a problem in the garden as well.

There are two main species of whiteflies, but they both cause similar problems. Severe infestations can cause leaves to curl downwards and yellow. Excessive honeydew production can also lead to sooty mold developing which can blacken the leaves, reducing photosynthesis. They are also known vectors of several viruses.

Control can be difficult because they are mostly feeding on the undersides of the leaves where they are difficult to reach with insecticidal sprays. That is also where the initial life stages or nymphs, which resemble small scale-like insects are attached and feeding on plant sap. Closely spaced plants can make trying to apply insecticides to the undersides of the leaves even more challenging. Heavily pruned plants may be more prone to infestation as well. Once the tomatoes begin to flower, we need to be carful of applying any insecticides that might harm pollinating insects. Insecticidal soaps can effectively kill whiteflies, but it must make direct contact with the adults or nymphs to be effective and it has no residual control. The best option is often to let natural predators consume the whiteflies. Encarsia formosa, is a predatory wasp that will readily feed on whiteflies. There are also several species of lady beetles that will eat them as well. However, heavily infested plants are likely best pulled and removed from the garden. Also, remember to check plants carefully for whiteflies when purchasing them in the spring at your local garden center.

Bugs on potatoes

Q Every year I seem to get these striped bugs on my potatoes but then I also see these smaller, pinkish bugs with spots, that are also eating the leaves of my potatoes. What are these bugs and how do I get rid of them? (See photo.) I have tried using Sevin dust, but it just doesn’t seem to do much anymore.

A These are the adults and larvae of the Colorado potato beetle. The striped adults overwinter in the soil, then emerge in the spring. They lay clusters of tiny orange eggs on the undersides of potato leaves. Once the eggs hatch, that is when the small, orange, spotted larvae come out and start feeding on the leaves.

Hand picking of the adults, larvae and squashing any egg clusters that you find can help reduce numbers and potential damage. Plants can withstand about 30% defoliation without much reduction in yield. It is important to rotate through different insecticides to avoid resistance to any one class of insecticides. While Sevin, with the active ingredient of carbaryl, was a good insecticide, it sounds like the beetles in your garden are now largely resistant to it. The key is to not repeat the same insecticide treatment repeatedly, or resistance is likely to develop. Look for other insecticides that contain Spinosad; Beauveria bassiana found in Botanigard; pyrethrins or pyrethroids. Bacillius thuringiensis var tenebrionis (Bt) a botanical insecticide is effective against small larvae (less than 1/4 inch) and should be applied at egg hatch or when larvae are first seen. Which ever insecticide you use, make sure to get thorough coverage of the plants. A liquid spray is going to allow for much better coverage than a dust formulation which tends to just cover the tops of the leaves and stems.

Zinnia plant in bloom. iGrow photo
Colorado potato beetle adult. iGrow photo
Coreopsis with yellow flowers. iGrow photo
The seedhead of crabgrass looks like fingers pointing upwards. iGrow photo
Whitefly on tomato leaf. iGrow photo
Amaranth plant in white pot. iGrow photo