The presence of a foamy droplet attached to the flower stems indicates the presence of a tiny green insect known as a spittlebug. It survives by sucking the juices from the stalk on which it is attached. The flower head on that stem usually will not fully develop. Spraying the foamy droplet with a burst of water and hand picking are two methods for removing the insect. The spittlebug is a nuisance but will not permanently or severely damage an otherwise healthy plant.
There are several plant diseases that harm lavender; however, their presence in our American gardens are not prevalent enough to cause concern.
The most common problem affecting lavender is the plant’s inability to transport water and process nutrients using its root system. This problem occurs when the soil becomes oversaturated and essential air pockets are clogged and displaced. This “gardener-created” situation essentially drowns the roots and eliminates their ability to regulate the movement of water and nutrients, respond to sunlight and temperature, and maintain internal plant pressure or turgidity. Over time, a soil borne pathogen known as phytophera may render the tender root hairs permanently incapable of transporting moisture and nutrients to the plant. It may take 2 to 3 seasons to observe the total damage that occurs from one or both of these conditions. Portions of the plant will die back, and larger stems will break freely from the base of the plant. Removal of the plant is the typical course of action. Replanting any woody perennial in an area of infestation is not recommended for several years. Most likely, that planting area was not originally suited for lavender growing.
The root system of lavender has adapted to survive in harsh climates without high fertility and moisture. Therefore, it must be emphasized that it should be protected from extreme saturation and encroachment by weeds. Cleanliness around the plant is equally important. Good air circulation and a lack of soggy leaves, dead weeds and debris around the plant will discourage the growth of molds and fungus around its woody root base. By definition and geographical location, we are situated in a mediterranean growing region, but not by much. Maintaining good drainage practices, maximizing sun and heat exposure and ridding the plant of pathogen and moisture laden debris will greatly assist in promoting plant vigor.
Symptoms of plant stress
During the growing season the leaves and stems of lavender may bend, curl, twist, become distorted or turn yellow. In most cases, the plant is responding to extreme swings in temperature, humidity or unseasonable rains. They will recover. Over saturating stressed plants in these conditions, especially during humid and hot periods, may shut down the root system entirely and may do greater harm than good. Always strive to create a garden environment that is close to the plant’s native area, one that has free draining soil, good sunlight, summer dry conditions, low humidity and good air movement.
Roaming foragers such as deer and elk do not list lavender as a food of choice. Damage to plants from these species is most likely to occur from hoof traffic than feeding. However, if the animal is extremely hungry it may nibble from your lavender garden.
Tender new growth, if exposed to a hard frost, may show signs of damage to a section of the plant. A healthy plant typically recovers and it may take the better part of the growing season for the green material to return. The tiny leaves of lavender do wither and experience a seasonable life and death cycle known as necrosis. Total die off of all leaves without new bud and leaf growth in spring indicates that the plant has died. Confirmation of plant death can be made by examining the inside of several stems. If the stems lack green and supple growth and snap easily the plant has died. Most lavender varieties retain a gray-green appearance during the dormancy period. However, some varieties such as lavandula angustifolia, ‘jean davis’ express very darkened foliage during pacific northwest winters.
Information excerpt from Dr. Lavender's Owner's manual and is provided by the Sequim Lavender Company, Sequim, WA. All rights reserved.