Disease name: Stigmina needle cast
Pathogen name: Stigmina lautii (fungus)
Hosts: Most common hosts include Colorado blue spruce (Picea pungens), white spruce (P. glauca) Less common hosts include: Norway spruce (P. abies), Oriental spruce (P. orientalis), and Serbian spruce (P. omorika)
Stigmina needle cast is one of three needle cast diseases found on spruce. Stigmina is not considered an aggressive disease. It is more commonly found on trees under stress due to drought or mites. It takes several years of infection and defoliation before the tree begins to decline.
Symptoms
The main symptom of Stigmina needle cast is discoloration and loss of needles. Infected needles prematurely turn tan-green to brown and then fall off of the tree. This can result in the canopy looking unusually thin for the species. It can take up to a year for the needles to discolor and drop from the tree. Newer growth might appear to be healthy. More needles are shed in the interior of the tree, where the needles are shaded and where conditions may remain wet for a longer time.
This disease can be diagnosed in the field using a hand lens. The fungus will grow out of the stomates (breathing pores) on the underside of the needles. Healthy stomates are white and produced in straight lines. Infected needles will have black fuzzy or hairy growths projecting out of the stomates.
Stigmina is frequently mistaken for Rhizosphaera needle cast. If the black growths from the stomates look smooth, rather than black and fuzzy or hairy, the needle is infected with Rhizosphaera kalkhoffii. Another way to tell Stigmina apart from Rhizosphaera is that Stigmina will produce spores in green needles as well as discolored needles. Rhizosphaera doesn’t produce spores until the needles have turned purple or brown.
Disease Cycle
The fungus that causes Stigmina needle cast overwinters as black spore-producing structures in the underside of the infected needles.
A mass of spores is produced and released during the two months when the trees put on new growth. The fungus will continue to produce spores as long as temperatures remain above 50°F.
The needles infected in the current year may produce the fungal fruiting bodies in the fall.
Management
Cultural Management
Limit the planting of susceptible trees and remove infected trees. Ensure good air circulation to keep needles dry. This helps prevent infection. Prune out dead and dying branches to improve airflow and remove inoculum. Rake up the fallen needles.
Ensure the tree is getting the appropriate amount of water for the species and the soil type. Avoid overhead irrigation to keep the needles dry. During drought, use drip irrigation to water the tree. Stigmina is more common in stressed trees.
Resistant Species
Some evergreens are resistant to Stigmina needle cast. These include pine (Pinus), yew (Taxus), arborvitae (Tsuga), juniper (Juniperus), cypress (Chamaecyparis), and fir (Abies).
Chemical Management
Fungicides used for other needle diseases can be effective. The fungicides need to be applied to protect the newly emerging needles during candle elongation and needle expansion.
The pesticide information presented in this publication is current with federal and state regulations. The user is responsible for determining that the intended use is consistent with the label of the product being used. The information given here is for educational purposes only. Reference to commercial products or trade names is made with the understanding that no discrimination is intended and no endorsement made by The Morton Arboretum.
For current pesticide recommendations, contact The Morton Arboretum Plant Clinic at 630-719-2424 or plantclinic@mortonarb.org.