For The Union-Tribune
Checks and balances occur not only in our government, but also in gardens that are rich in beneficials and lush in plant diversity. These gardens benefit from a harmonious interplay of checks and balances that keep pests and diseases controlled.
My late mother-in-law had some favorite sayings. Her quick, favorite response to people complaining about troubles or disputes with others was, “It takes two to tango.” But in the garden, trouble with fungal disease or pest infestation requires not two but three essential factors to tango. When all three components are present in the garden concurrently, they make up what is known as the disease triangle. The three components are:
A. A susceptible host.
B. A conducive environment for the pest or disease to thrive.
C. The presence of a pest, or a disease pathogen that is virulent and has the ability to infect and colonize a host and to reproduce.
In life, we cannot change others, but we do have the ability to change ourselves and our responses to trouble. The same principle applies in the garden. We might not be able to prevent the third component, the presence of a pest or virulent fungal disease, but the first two components of the disease triangle are within our control. We must NOT plant a susceptible host, and we must NOT allow a conducive environment in our garden for the pest or disease to thrive.
Follow these steps to thwart the disease triangle:
On disease-susceptible roses, black spot can develop in wet weather, high humidity or conditions like overcrowded plants that prevent foliage from drying. Black spot is identified by the feathery margins of black spots on the upper surface of leaves. (Rita Perwich)
Select hosts that resist disease
Plants’ resistance and response to fungal and pest attack varies with different rose cultivars. Some roses are susceptible to fungal pathogens such as rust, black spot and botrytis. Roses susceptible to rust and black spot may defoliate, and the plants often bloom poorly, if at all. In cool, wet weather, petals on roses susceptible to botrytis often have gray or brown edges and some buds on the plant will ball up and not bloom.
Other roses are not susceptible to these diseases because they have genetics that are resistant. Selecting these hardy roses for our garden is worthwhile, because a rose that is not a susceptible host will not develop disease even when the pathogen is present and virulent. Roses that are not susceptible to disease are usually more able to withstand pest damage.
I have some roses that bloom well and remain vigorous despite getting rust, black spot and botrytis. These roses are not nonsusceptible hosts, but they are tolerant. Tolerance is not equivalent to resistance, but when the rose is performing well, this hiccup seems small and is easy to overlook. But we must compensate by taking extra care to keep the disease in check by conscientiously removing diseased leaves, buds and blooms from the garden.
Plants that are susceptible hosts and intolerant should be dug out and eliminated from our garden.
Lyda Rose is a highly rated garden rose and has wonderful resistance to fungal diseases. (Rita Perwich)
Promote a setting that curbs disease
We can simultaneously thwart diseases and pests of the conducive environment they require to thrive and provide our roses with a healthy environment to flourish when we address the following in our rose garden:
Sun: Roses must be planted where they will get six to eight hours of sun exposure daily. When smaller roses are being shaded by larger roses, they should be transplanted.
Good soil: Roses should be planted in a well-draining soil that is amended annually with organics such as compost or worm castings and topped with several inches of an organic mulch.
Pruning: Annual pruning removes dead and damaged canes and opens the plant up to air and sunlight. Throughout the growing season, we should cut out clusters of dense foliage growing toward the inside of the bush. This clutter can promote disease and provide hide-outs for pest infestations.
Air circulation: Roses require good air circulation and the rapid drying of their foliage. When roses are touching, they should be staked or pruned.
Spacing: Allow adequate spacing when planting. When our roses grow larger than we anticipated and outgrow their space, we need to consider transplanting them or the other roses they are cramping. Roses with an outward sprawling habit like Princess Alexandra of Kent can be trained to grow upright by pruning some canes to an inward-facing bud eye.
Appropriate irrigation: Disease-susceptible roses require only two hours of moisture to develop rust and six hours of moisture to develop black spot. Irrigating and spraying water on our roses’ blooms and leaves for pest management in the morning gives leaves time to dry out and shortens the time that foliage is wet, to prevent water-initiated fungal diseases. A drip system that delivers water to the soil is preferable to overhead watering.
Sanitation: Blooms and leaves on the plant exhibiting symptoms of fungal disease and pest damage must be cut out. Removing leaf and petal debris from garden beds minimizes the presence of diseases and pests.
Should it stay or must it go: Fungal diseases are hard to control in overcrowded rose gardens. If our garden is overcrowded, we need to face up to the hard task of removing some roses. When we give in to the temptation to buy new roses and our garden is already jam-packed, a disciplined approach is to dig out an equal number of roses. I am the first to admit that this advice is easy to give and very hard to follow!
Shovel-pruning: Our gardens are much healthier when disease-magnet roses are shovel-pruned.
Take extra care to avert trouble
Watchful gardener sleuths look for the following signs, symptoms and clues and follow up with appropriate action to keep pests and diseases in check. These actions keep our plants stress-free and healthy. Healthy plants better withstand disease.
• Lacy leaves? We turn the leaf over and look for bristly rose slugs. We squish them.
• Tattered and chewed leaves and blooms? We look for caterpillars, grasshoppers, katydids or beetles. We catch them and use our pruners or fingers to dispense with them. We drop beetles in soapy water.
• Twisted, crinkled, yellowed or bronzed foliage or squiggles in leaves? Sucking insects such as leaf hoppers, aphids, thrips, chilli thrips and leaf miners are the culprits. Stippled leaves and fine webbing on the underside of leaves are our clue that spider mites are at work. We squish the insects we see, and we cut out and remove the damage caused by the ‘’invisible pests. We use blasts of water from our hose to eliminate spider mites and aphids.
• Black spots, orange pustules, white powdery coating on leaves? Blooms balled up or petals browned, bruised or spotted? These are indications of common fungal pathogens that must be cut off the plant and removed from the garden.
Plant diversity entices beneficial insects into the garden and minimizes and checks the spread of the fungal diseases that plague roses that are grown in a monoculture. (Rita Perwich)
Plant diversity entices beneficial insects into the garden and minimizes and checks the spread of the fungal diseases that plague roses that are grown in a monoculture. (Rita Perwich)
The double-duty benefits of plant diversity
The health of our plants is maximized when beneficial predatory insects, birds, spiders and lizards inhabit our garden and help check, balance and minimize pest damage. Plant diversity in the rose garden does double duty. It not only entices these beneficials and pollinators into our gardens, but it also minimizes and checks the spread of the fungal diseases that plague roses that are grown in a monoculture.
Nature’s checks and balances — and our proactive decisions and quick actions to obstruct the triangle’s lines from being drawn — allow our plants to flourish. Taking out just one of the three factors of the disease triangle thwarts and checkmates pests and diseases. Two to tango loses its connotation of trouble and becomes instead a joyful, harmonious dance between the gardener and their healthy garden.
Perwich is a member of the San Diego Rose Society, a Consulting Rosarian and a Master Gardener with UC Cooperative Extension.