The Ultimate Pest Control: Diversity

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A little helpful information:

Gardening in our climate is not just about the weather. Pests and diseases can interfere with our personal Eden. Since the weather has slipped into boring November mode (as opposed to exciting November mode) I thought I’d pass on a few observations that I hope will add to your gardening knowledge.

Yer really buggin’ me

For the most part avoiding plant pests is easily 75% dependent on correct culture. We all know that if you don’t want aphids you should probably avoid Roses. The healthier a plant is the less it will be bothered. Grow plants to their ultimate cultural requirements and that is the ultimate pest control.  But several excellent plants are afflicted and for the most part they shouldn’t be chucked out completely.  Hellebores are one such perennial that inevitably suffers aphids. They almost always do and though it can be gross to us humans there is an easy solution. Do almost nothing. OR spray the aphids off with a strong jet of water. I have found over the years that resorting to poisons is a worthless, costly, and dangerous way to spend your time. The plant industry is heavily founded on the predication that gardening is a problem that needs to be solved. They will happily sell you any kind of dangerous concoction to fling about your beautiful space. The truth is: its not necessary. So, in the case of Hellebores- where the aphids do almost no damage, either spray them off with water- they are soft bodied insects and this will damage or kill them or do what I do. Simply ignore them. By winter when it is time to cut back the foliage to make way for the flowers the aphids will have disappeared. POUF!

Protect the predators and you will win

Lady Beetles (Lady Bugs) – especially their larvae eat aphids. They should be encouraged to proliferate. By the way, the larvae look like little black alligators. They cannot fly and scramble around the plants foraging for aphids. Even Yellow Jackets will consume aphids so they have in part some reason for existence. Ants will farm aphids- they will actually physically move them to the soft  tips of the plant. Aphids are born pregnant by the way which relates to their seemingly overnight increase.  Don’t go killing the ants- again spray water or squish the aphid populations at the tip with your fingers and you will have progress. There are various other critters that can make a home. Luckily, in our climate- unlike the east we do not suffer Japanese Beatles or other voracious things. There are exceptions and they do turn up from time to time. An example is the Marmorated Stink Bug which has recently leapt to our shores. It tends to gather in great numbers on specific plants. You can easily identify this guy – as opposed to other shield plated green stink bugs by the fact that it is brown and the prominent antennae are striped horizontally. They are attracted to felty leaved things such as Clerodendrum and Paulownias. For the most part they do very little damage other than to mass and gross us out. Already their numbers are declining from natural predation. They can cause problems for home food growers- a topic of which is outside the scope of this blog- flowers man, its about flowers. So, it should be obvious that spraying poisons kills the good guys as well as the bad. No need to upset the balance and cause potentially long lasting harms. Let it be.

Slugs piss us off

Slugs (and snails) can be a real pain on attractive plants and they are part of the cost of doing business in our region. Personally, they are not a huge problem in my garden because I now avoid plants that call them in. Hand picking slugs in the evening on susceptible plants is one way to lower the population. It may seem futile, but trust me the amount of damage that a single slug incurs is more than you think. Many slugs spend their  day time in the soil beneath the plants. Mulch and tidiness are a great help here. Cultivate the soil gently around Hostas and you will find the hungry culprits. Slugs are especially damaging to plants that are just emerging. Focus your energy there and the plant once up and growing can withstand attack.  There is slug bait which can work very well if you are persistent. Sluggo (TM) is not toxic to pets and it does work- but it must be applied constantly- preferably in mid spring and though slow it really will put a dent in the population. As an aside in the past I have used metaldehyde (Deadline) when the whole gastropod thing was totally out of hand. The ONLY way to use it is to put it in the bottom of a bottle or jar and lay the container on its side. The bait will lure them in and the container will protect pets who are also attracted to the lethal goo. Simply discard the container when it is full of slug holocaust. Snails are just as pernicious as slugs and hand picking is surprisingly affective. You can also make traps. One way is to take a 2″ x 4″ and pour beer on it. Then prop it up with two bricks. During the day the snails and slugs will congregate in the shade on the underside of the board. Simply pick and dispatch the offenders.

Some perennials that are resistant to slugs: Geranium, Dicentra (Lamprocapnos), Epimedium, Vancouveria,  (The Hosta cultivar ‘June’- shows remarkable resistance), Oxalis oregana, Ferns (nearly all), Euphorbia rigida, Cyclamen coum, Hybrid Hellebores.

Stupid little notches

The Strawberry Rootweevil is a pest that shows its presence in several different ways. Most conspicuously notching of the leaves of broad leaved evergreens is a sure fire indicator. As an adult the shiny black 1/4″ long weevils are surprisingly slow and dumb. They are active at night and I’ve gone out and shaken the bushes to watch them drop lethargically onto the ground. Put a pillow case under the shrub and do this and then simply squish the dumb things. They move pretty slow. More damaging is the larval stage. They insert themselves into the root mass of plants and feed. Obviously strawberries are one of the victims but I have found them on nearly everything- perennials, shrubs etc. They may feed so heavily that the plant collapses or loses enough root mass that it appears drought stressed. By then its too late. But there is great control with predatory nematodes. This should be applied as a liquid. They come on little sponges (avoid exposing the sponges to large swings in temperature) Simply place the sponge in a watering can and then pour around the base of the plant. They require liquid to travel through the soil so don’t let it dry out. Weevils seem to prefer dry shade conditions. Regular watering and mulch and healthy plants appears to dissuade them.

The soil giveth and the soil taketh away

Nothing is more disheartening than having a plant up and croak. Believe me it happens to ALL gardeners in ALL gardens. Often it is a complete mystery and the best way to deal is to simply move on- plant something new and commit the dead to the garbage. It could be culture, it could be the way the plant was raised to begin with, its possible that an errant gust of wind rocked the plant and tore the roots. No reason to over think it. Here are some culprits that really do warrant attention.

I’m rotting, I’m rotting.

In our region there are two soil borne pathogens that really can wreak havoc. They are Phytophthera and Verticillium (wilt). They are either present in your garden soil or they are not. Phytophthera is almost universally present in my experience. It causes root rot and it can seemingly snuff out a plant in a day or two. It forms masses of threads in the soil that are tiny – don’t go trying to locate the threads- and the spores travel through water in the soil. It can be introduced from moving a plant (with minute amounts of garden soil on the roots) from one garden to the next. But as I said, chances are that it is already present. It is greatly exacerbated by over watering or watering when the temperature is high. A plant may  live happily and then simply collapse in a short period of time. I wish there was a comprehensive list of everything that is susceptible- and there are many things that are not- but with so many zillions of new plants on the market I somehow doubt they would all be covered. Plants native to summer dry climates are the most at risk- as well as drought tolerant plants to begin with. Here is where culture and plant origin dictate how you grow them. Avoid watering a drought tolerant plant on a hot day. ( Watering to establish a new plant is different- water until you see new growth, then taper off)  Some plants that are susceptible are our native Chamaecyparis and its millions of cultivars. (Chamaecyparis lawsoniana), Grevilleas, Ceanothus, Arctostaphylos, Cotinus- you see a pattern. Here is a little more information that I found:

“Plants typically die from phytophthora dieback at the end of summer when the plants are under the most stress. For this reason phytophthora dieback can often be confused with symptoms of drought. Phytophthora dieback will affect a range of different susceptible plants, but will not impact on resistant plant species. If the disease is suspected, a likely mode of disease transmission should be identified. The best method to confirm the presence of the disease is testing of soil and/or plant samples by a diagnostic laboratory.”

Skip the laboratory. Do not over water drought resistant plants- in this case that CAUSES stress. And I have found that even a small amount of water on a hot day can spell disaster. Instead, rely on a plants natural adaptation to dry conditions. Let the plant rely on all that falls from the sky. In winter when soil temperatures are cool Phytophthera is not an issue. If a plant succumbs to this you can choose to NOT replant with the same thing- if your Daphne croaks, do not plant another Daphne there – thats just common sense. Try for a completely different genus. Experimentation and diversity are the key.

I’m wilting, I’m wilting.

Verticillium (wilt) is also present in many garden soils. It manifests itself differently. Instead of taking out the whole plant- it does it in irritating stages- Its hallmark is one dead branch at a time. This too has a long list of plants that are susceptible and a list of tolerant plants. Verticillium infects the tissue by plugging it with mycelium spores on the interior wood- girdling one portion of the stem at a time. It is known as a wilt because that is how it presents. Japanese maples are frequent victims as are Hebes. There has been some success in using well composted mulch to diminish its affects. Dormant in the winter it arrives with the warmth of spring. The best recommendation I can make is again to plant for diversity- if you are replacing an afflicted plant- remember to make it a different genus. If your maple is affected consider a Crape Myrtle, they are resistant and one of the reasons we grow them. Other good choices are Nothofagus antarctica, Trochodendron aralioides, Eriobotrya japonica, Gingko biloba, Metasequoia glyptostroboides, Ceanothus and Feijoa.  Once again, this is where diversity is your friend. Monoculture- as we know has its drawbacks. Think differently. If you do choose to mass a plant take a moment to find if it is resistant. Again, as with Phytophthera a stressed plant will be the first affected. This is where grouping plants together with similar requirements pays dividends. Dry with dry, wet with wet. I have seen plants recover from this- prune out the affected tissue with a sterilized pruner and make sure to sterilize it again before its re-use. Use mulch to moderate the ground moisture and temperature. Avoid stressing a plant.

Diversity leads to a healthy garden

The key to avoiding pests and disease is through diversity in our gardens. Pay close attention to the ultimate cultural conditions of a plant. Consistency is also a healthy way to approach growing plants. Group those with similar requirements together. It all comes down to having a plan. That may be easy to say but less easy to live. If a plant succumbs to a disease- do not plant the same genus- move on. The greater diversity of plants in your garden the less likely you will suffer devastation by pests and disease.  A good garden steward knows how to roll with the punches. Pests, disease, weather are all part of the great outdoors.


The Ultimate Pest Control: Diversity

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