Why are my hemlocks yellow

Fall needle drop is a normal part of a conifer's seasonal cycle. It has been a summer and fall of record high temperatures and dry spells so the phenomena is particularly pronounced this year and may strike you as something unusual.

You will probably notice that the brand new growth is not particularly affected but it is more interior, older needles browning. They remain on the tree for several years then turn yellow and brown, looking unhealthy for a few weeks before dropping. If you notice that newer, branch tips are browning in significant numbers or see any cankering or lesions on the branches that are browning I do not see any of that in your photos , that is more worrying and time for a visit from an arborist.

If you google "conifer fall needle drop" images, you will see photos that should reassure you. Thank you so much for your response! Roots in flooded or waterlogged soils are damaged and die from oxygen deficiency. Feeder roots are particularly sensitive and are frequently the first ones damaged.

When roots are damaged, they are unable to provide water to the top of the plant. Damage can be sudden or gradual, depending on the plant and the flooding conditions. This can occur on plants in obviously wet sites and on those in marginal sites or soils such as along city streets or in areas where high clay content in the soil impedes drainage. Most trees cannot grow in waterlogged soils for very long and can die if flooded for only a few days during the growing season.

Visible symptoms are often not evident until considerably after the damage has occurred, especially when the root damage is gradual.

Seedlings and new transplants are more sensitive than established plants and gymnosperms needled evergreens are generally considered more sensitive than angiosperms. Top symptoms may not develop until water demands increase during the hot summer months. Other evergreens appear to lose vigor and slowly decline over a period of years. This can occur on trees that have been otherwise "healthy" for 10 to 15 years but are growing in poor sites or heavy soils. Dormant plants generally appear to tolerate flooding longer than those in active growth.

In addition to direct root damage, trees in flooded soils are predisposed to secondary root-rot pathogens and other opportunistic pests. Strategies for minimizing wet soil problems include: 1 selecting an appropriate site and following proper planting practices; 2 cultural practices that maintain plant vigor and stimulate growth; 3 selecting appropriate species for soil and site conditions: water-tolerant larch versus water-intolerant spruces, hemlocks, yews ; and 4 pruning dead or dying tissues to minimize secondary invaders.

Drought or dry soil conditions resulting in feeder root damage and death contribute to the development of water deficits in plants. Symptoms are manifest in different ways, but are often not evident until some time after the event has occurred— even as much as a year later!

Effects are particularly severe on seedlings or new transplants because their roots occupy the uppermost layers of soil where the most rapid drying occurs and are compounded by the loss of feeder roots during the transplant process.

Females in both species do not fly and are moved around primarily by wind and birds. Unlike hemlock woolly adelgid, which can easily be seen because of the cottony masses they produce at the base of needles, the elongate scale is much more subtle. Both insects damage hemlocks in much the same way. These two pests can often be found together and can have 2 generations each year, so regular treatment is necessary to maintain populations at a minimum.

There are topical and systemic options for treating these pests. The adelgid and scales do not move once settled on a branch or needles. For this reason, they can be treated very effectively with horticultural oil in most cases, which works merely by smothering the insects in place.

Horticultural oil can be made from petroleum, but we choose to utilize organic mineral oil for these applications. With heavy infestations of these insects or in places where trees are very large or spraying is not feasible because of drift concerns, trees can be treated with a systemic insecticide. A systemic insecticide can be applied to the lower portion of the trunk of the tree where it is absorbed and spread throughout the canopy. One application will last the entire season.

In cases were elongate hemlocks scale is more prevalent this can be a good alternative or supplement to a spray program. Though systemic insecticides in the class of neonicotinoids can be harmful to bees, when applied to the trunk of the tree, exposure is limited.