Got holes in your leaves? Don't reach for the insecticide that is guaranteed to kill a wide spectrum of different insects or the Bacillus thuringiensis (just kills caterpillars) until you know what the culprit is, or you may just destroy a beneficial insect instead!

Leaf cutter damage to peony leaf

The leaves of some of the plants, in my herbaceous borders frequently develop a tessellated appearance around the edges due to the nibbling of leaf-cutter bees (megachildae), and when other gardeners come to visit I am surprised at how few people recognize the very distinctive pattern on the leaf edges.   Roses and peonies are the most frequently visited, and quite often only a particular stem of leaves on a plant appeals to them. In a garden that I tend and which has a collection of roses only one plant is ever used and nearly all the leaves on that plant have been much chewed while the others are untouched.

If bees visit flowers for nectar and pollen why on earth are they chewing on leaves? Well this particular species of bee lays its eggs in holes in wood, often using old beetle holes or bug hotels, then fills each hole with pollen and resin to provide food for the larvae and finally seals the hole with a piece of leaf or flower petal.

 

Generally speaking leaf-cutters do little damage to the plants that they harvest from so no action needs to be taken to control them. However, this spring I installed a pollinator-friendly garden which included a very small 'Rising Sun' redbud tree. I don't know if it was the citrus-colored leaves that appealed, but beginning in July every new leaf was quite severely damaged and our bee house was very artistically decorated, implying that my pollinator garden was a great success for at least some species.

The pleasure that I get observing the many different species of bees in the garden far outweighs any damage that they do, so no sprays will be used, and if the damage becomes severe I can put a fine mesh net over my little tree until it becomes established.

Our dry climate on the east side works wonders to control fungal diseases. Most fungi prefer moist environments. While we still get an occasional fungal pathogen, we seem to have greater problems with insects and viruses. In many cases the insects and viruses team up to cause real mayhem in the garden.

In our area we have been subject to continual attacks on tomatoes by viruses. Our most common viral issue is beet curly top virus spread by the beet leafhopper. It is widespread from Coso Junction through Bishop. You may be familiar with its distinctive symptoms: curled up leaves, possibly with a purple tint, along with small, undersized fruit. But it isn't the only viral issue we have to deal with. 

Of lesser importance in our area is tomato spotted wilt virus (TSWV), but this year it has had a good showing in the Owens Valley.

This virus can affect dozens of plants, but tomatoes, being so common, are the most usual victim reported.

The easiest symptom to recognize is the distinctive color pattern on ripe fruit. (See picture.) If you see this (probably with some leaf spots) there is a good chance this virus is the culprit. 

In some cases the virus attacks early or is more virulent and does a number on the foliage and new shoots. The leaf symptoms start on new shoots and at first may look bronze, eventually turning into dead spots. On tomato I usually see these spots more toward the base of the individual leaflets, but this isn't always the case. Other crops respond differently. Sometimes the virus kills shoots entirely! By the time I usually get to see the plants the disease has progressed to the point where there is a mess of dead shoots, and half-dead leaves. I cross my fingers and hope there is symptomatic fruit for me to see. Viruses can be hard to diagnose by symptoms alone.

This virus is spread by tiny, hard-to-kill insects called thrips. Unless you have eagle eyes, you'll need a lens to see them. These small insects have frilled wings and rasping mouthparts that tend to tear up new buds and leaves, leading to malformed growth. While feeding, they infect the plants with the virus. Even if you kill the insects, once infected the plant is a goner.

So what do you do? First look for symptoms to confirm this is the problem. I usually check to see if there are thrips present as well with a hand lens or microscope. If I'm sure I have the virus I remove the infected plants and try my best to control the thrips population. UC IPM suggests insecticidal soap. 

I wouldn't lose a lot of sleep worrying about whether my garden was going to be attacked. Some years are worse than others. Keeping weeds under control and watching for pests diligently is your best plan. Using yellow or blue sticky traps in the plant canopy is a good technique to monitor insect population. 

As always, if you aren't sure what's going on, please contact the Master Gardeners at immg@ucanr.edu for help. 

Beat the Cheat

Part II: How to get rid of cheatgrass!

Part One of the cheatgrass story informed us of its invasive weed status and how it creates a fire risk around the home. But there is hope.

First, remember that any disturbance of the soil is an invitation to cheatgrass - maintaining an adequate cover of native plant species and biological soil crusts can render some communities more resistant to cheatgrass invasion.

Where soils have been disturbed, however, you must remove live plants and prevent seed production. This takes hard work and persistence and then more persistence! For small areas, hand pulling is effective if done diligently over many years. Cheatgrass is typically a winter annual grass. It grows early and rapidly (often before other annuals germinate) and is fairly easy to identify and manually pull during the cool temperatures of late winter and early spring, especially when it first appears.

For areas where mature communities persist, I have developed a 2-year eradication plan that works well. First, I lift the roots out of the ground a few inches below the soil (these fine, dry roots at the surface are another fire hazard) with a soil knife and remove as much of the plant, seeds, and roots as possible. Yes, the seeds germinate better in the light and fluffy soil left behind so I tamp down areas I have weeded to condense the soil structure. Once these nests of old grasses and seeds are gone, it is much easier to remove the new plants that might come up in year two (and three, and four...). You can also use a hula hoe but remember to rake up as much of the plants, roots, and seeds as possible.

If there is a community of cheatgrass that goes to seed before you have time to remove the plants, your neighbors will thank you if you at least remove the seeds. Using a string-trimmer when the seeds are still immature can be effective to reduce seed spread but you still need to go back and remove the plants so they do not regrow and to reduce the fire risk.

For larger infestations, chemical controls or grazing should be considered. Be careful using herbicides because those recommended for controlling cheatgrass can also harm nearby native species. UC IPM has information on controlling brome grasses including timing of herbicides, if used. Grazing by goats is another option. Grazing during the spring and fall must be used for at least two consecutive years to be effective.

The use of mechanical equipment is not recommended because it disturbs the soil and may exacerbate the problem. So plan some time for some old-fashioned weeding to get rid of this pest of a plant.

 

For more information:

• USDA and US Forest Service Fire Effects Information System (FEIS)
• USDA Field Guide for Managing Cheatgrass in the Southwest
• UC IPM Page on Brome Grasses
• UC IPM Invasive Plant Page
• UC IPM Managing Weeds in the Landscape

Beat the Cheat!

Part I:   Why cheatgrass is so very bad!

Each year, my number one garden task is working to get rid of all the cheatgrass that moves in. Cheatgrass (Bromus tectorum) is an aggressive invasive species that thrives in disturbed soils. How aggressive? Each plant produces between 25 and 5,000 seeds which remain viable in the soil for 2-3 years. Density of cheatgrass averages 600 plants per square foot and it is not uncommon for plants to produce two seed crops in one season. Can you do the math? These plants are prodigious!! And once established, cheatgrass communities can persist for decades.

Cheatgrass is found throughout California and is the dominant annual grass on sagebrush rangelands in the Owens Valley. If you live on the edge of the wildlands, cheatgrass seeds constantly blow onto your property and present a perennial problem no matter how carefully you weed your yard.

The reason cheatgrass is so very, very bad in the garden around your home is because it presents a great fire risk - igniting easily and spreading fire rapidly. Cheatgrass has a very fine structure, accumulates litter, and dries completely in early summer, becoming a highly flammable, often continuous fuel. Cheatgrass promotes more frequent fires by increasing the biomass and horizontal continuity of fine fuels and by allowing fire to spread across landscapes where fire was previously restricted to isolated patches. And because cheatgrass loves disturbed soils, wherever we leave our mark on the land, cheatgrass soon happily follows: lots that have been cleared for home construction, areas that have been cultivated and subsequently abandoned, plots with excessive livestock grazing, areas where the native overstory has been removed, and even repeated fires can interact, or act singly, to proliferate cheatgrass.

That's the bad news. But there is hope for our landscapes. Stay tuned for part two, how to get rid of cheatgrass!

 

For more information:

USDA and US Forest Service Fire Effects Information System (FEIS) -

https://www.fs.fed.us/database/feis/plants/graminoid/brotec/all.html