The beautiful needles of the Blue Spruce are not only the object of desire for many homeowners but also a target for various parasitic organisms.
QUICK ANSWER: The main reason why Blue Spruce turns brown is the Rhizosphaera needle cast disease. Remove any damaged parts along with the fallen needles and spray with copper fungicide several times to cure Blue Spruce.
Rhizosphaera Needle Cast
Rhizosphaera needle cast is a fungal disease. When the pathogen gets on the needles, it begins to germinate, and the needles die. The disease spreads most strongly in humid and warm weather. Poor air exchange around the spruce also contributes to its development.
Read also: Colorado Spruce Grower’s Guide
Symptoms:
The needles on two-year-old branches turn brown and fall off. The annual growths often remain healthy. It can be said that the Rhizosphaera needle cast affects the inner branches while the outer ones look healthy.
But this is not always the case; sometimes, the whole branch is affected simultaneously. The needles from the trunk to the tips turn brown and fall off.
If you look closely at the needles, you can see tiny black spots. This is the body of the fungus.
Treatment:
- Cut off the dry branches and collect most of the fallen needles. Burn it all or throw it far away from human homes.
- Spray Blue Spruce with an aqueous solution of copper fungicide. Do this thoroughly, and don’t miss any branches. Also, spray the trunk inside the crown.
- Repeat the spraying after 2 weeks. This time, use Chlorothalonil-based fungicide.
- Several sprays may be needed throughout the growing season—alternate fungicides to get the best effect.
Cooley Spruce Adelgid
Cooley Spruce Adelgid are pests of Blue Spruce. These insects have a rather complicated life cycle and need two hosts.
The female lays eggs near dormant buds in spring. When young branches emerge from buds, the larvae have already hatched and start to feed on young needles. Next, the larva penetrates the young growth, and gall forms.
The larva feeds on the branch from within, and eventually, the gall will shrivel up and turn brown.
Symptoms:
Young branches begin to get thicker and swell. This is how the gall is formed with the larva inside.
Over time, the gall will shrivel up and turn brown. A new insect emerges from it.
Treatment:
- Remove all the galls from the Blue Spruce and burn them.
- Spray the healthy needles with horticultural oil.
- For severe infestations, use a systemic insecticide.
Spider Mites
The next cause of needle discoloration is mites. These are tiny creatures that parasitize on needles and branches by sucking their sap.
They are most active in dry, warm weather. They can stay on a plant for a long time without being noticed, but their population quickly increases as soon as favorable weather arrives.
The needles turn brown much slower than in the case of disease, so the mites are not immediately noticed.
Symptoms:
The needles are pale and do not look healthy. After a while, the color changes to light pink but does not fall off.
Next, the needles turn brown and fall off. Very fine cobwebs can be seen between the needles.
Treatment:
- Wash the mites off with a hose, as they do not like moisture.
- Spray the needles with an aqueous solution of neem oil. Repeat the spraying after 2 weeks.
- If the neem oil doesn’t work, use acaricide (miticide).
White Pine Weevil
White pine weevil is also a common cause of needle browning. Adults usually feed on needles on last year’s branches. Females lay eggs near buds in early spring.
When young shoots grow, the grubs penetrate them and feed on young tissues, making tunnels. As a result, the current year’s shoots droop downward. After some time, they shrivel and turn brown along with the needles.
Symptoms:
This pest usually damages the very top of the spruce. Young, immature shoots droop toward the ground. The needles turn brown and fall off.
Treatment:
- Remove dead shoots from the tree and destroy them to prevent the grub from becoming an insect.
- Spray the needles with a systemic insecticide. Repeat the spraying after 2-3 weeks.
- Clean all plant debris under the spruce together with the insects that are there.
Browning after transplanting
The needles may change color to brown after planting or transplanting a Blue Spruce. If you plant spruce at the wrong time (summer), the roots may not give the needles enough water and will change color.
Also, if you move the spruce to a new location, you will change the sun exposure. As a result, it may get more sunlight and get a little burnt. Although the Blue Spruce can withstand full sun, sudden changes in light can cause damage to the needles.
Symptoms:
- The needles turn brown after planting in a new location.
- Planting was done in summer or very hot weather.
- Roots were severely damaged during transplanting.
Solution:
- Plant and move Blue Spruce only in early spring or mid-autumn.
- When transplanting, avoid damaging the root system.
- After planting, place a shade over the spruce for 3-6 weeks.
- Water when the soil is more than 1 inch dry.
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