Master Gardener Logo

Cass County Extension

Cass County Logo


Insect, Disease & Other Problems


A) Fire Blight (Apples, Crabapples and Pears)
               - worst on vigorously growing trees
               - spring and early summer; after hail storm
               - shepherds crook; leaves brown and remain attached
               - flower clusters and twigs blacken
               - overwinters in cankers on trees
               - pencil size or smaller twigs are killed by winter cold
               - larger diseased areas must be pruned off a few inches below disease
               - disinfect cut surfaces and equipment with 10% bleach solution
               - raspberries can also be infected.

    B) Apple Scab
               - dark green or gray (sooty) spots on leaves
               - fruit; first slightly raised brown spots; later - deforms and cracks
               - overwinters in fruit and leaves on ground - clean up fallen leaves

    C) Cedar Apple Rust
               - apple and red cedar (overwinters)
               - don't plant red cedar within mile of apples
               - brown corky spots on apple leaves; most fruiting cultivars are resistant

    D) Black Rot
               - invades old wounds and sunscald cankers; girdles trunks and limbs
               - pinhead sized black fruit bodies on the bark; often arranged in rows
               - frog-eye leafspot; black rot organism attacking leaves
               - spots have purple margins and tan to brown centers
               - also attack the fruit; blossom end rot or mummifies and hangs on tree
               - clean up sunscald areas and cover with tree wound dressing
               - remove all brown and discolored wood; sterilize pruning equipment
               - remove mummies

    E) Powdery Mildew
               - attacks many different plants
               - white powder on leaf surfaces
               - favored by cool wet weather and poor air circulation
               - prune to thin out branches and leaves

    F) Blackknot
               - plums & cherries
               - black knots form on twigs, branches & trunk
               - remove as soon as found; spray with lime sulfur in early spring

    G) Perennial Canker
               - attacks stone fruits
               - first noticed as sunken and slightly darker bark
               - large amount of resinous material oozes from the cankers
               - prune out all dead and weakened branches
               - avoid excessive use of nitrogen; avoid wounding trees

    H) Plum Pockets
               - fruits are enlarged, swollen and bladder-like
               - remove and destroy diseased fruits and plant parts
               - dormant spray of lime sulphur; before buds swell in the spring

    I) Brown Rot (Stone Fruits)
               - brown spots on fruit; later fruit becomes puffy and distorted
               - overwinters in diseased fruits; use good sanitation methods

    J) Black Rot on grapes
               - berries shrivel, dry and discolor when half-grown
               - use good sanitation methods in fall

    K) Downy Mildew
               - disease of grapes
               - yellowish green spots on leaves; white downy growth on bottom
               - fruits may also be infected; light brown & fall off
               - over winters on dead leaves; sanitation

    L) Antracnose or Cane Spot
               - disease of raspberries
               - first appear as small purplish raised area; enlarge and become sunken
               - gray to white spots; up to inch diameter on canes
               - leaves may also get tiny brown spots; centers of spots may fall out
               - prune out infected canes; winter sanitation

    M) Cane Blight
               - brown or black on one side of the cane
               - extends up or down several inches eventually surrounding the stem
               - lateral shoots grow poorly, wilt and die in hot weather

     N) Spur Blight
               - small brown or purple spots on lower nodes; leaves and flower buds die
               - diseased canes dry and crack as they mature
               - leaf symptom: dead brown wedge-shaped areas
               - provide good air circulation around plants

     O) Strawberry Leaf Spot
               - circular spots on leaves, 1/8 to 1/4 inch across
               - with purple borders and tan centers
               - more common in wet conditions

      P) Strawberry Root Diseases
               - Red Stele and Black Root Rot
               - common in heavy poorly drained soil; don’t over water or keep too wet
               - plant resistant varieties

      Q) Strawberry Fruit Diseases
               - Gray Mold & Leather Rot
              - attacks any part of the strawberry which touches the ground
              - another decaying fruit or a dead leaf
              - also attacks blossoms and immature berries; mulching may help
              - don't allow over crowding of plants and avoid heavy spring fertilizing
              - leather rot; mature fruits are tough, leathery and often bitter tasting

      R) Apple Maggot (Railroad Worm)
              - small fly may lay egg into fruit any time from late June through August
              - larvae tunnels through fruit and drops out when mature
              - fruit has a bumpy outer appearance and fine trailing running through it
              - pick up and destroy apples which drop early
              - hanging red ball-shaped traps in the tree will help; coat with tangle-trap

      S) Curculio (Apple or Stone Fruits)
              - snout beetle deposits egg into fruit; leaves a crescent shaped scar
              - more problem in deep shade
              - wormy plums turn red early and fall; apples are distorted
              - pick up and destroy all fruit which falls early

      T) Raspberry Cane Borers
              - black beetle lays egg into young cane
              - girdles stem just above and just below point where egg is inserted
              - tip of shoot wilts and dies shortly after being cut
              - remove wilted tip as soon as noticed
              - cut an inch or two below the lower girdle ring

      U) Raspberry Sawfly
              - larvae eat holes in leaves; feeds for less than two weeks
              - usually not a serious problem

      V) Spider Mites
              - suck sap from plant leaves which become somewhat mottled in color
              - can be a serious problem on raspberries especially in dry years
              - to control spray or wash undersides of leaves weekly for three weeks

      W) Sap Beetles (Picnic Beetles)
              - feed on ripe and over ripe fruits; control is difficult due to time of attack
              - raspberries, strawberries and many other crops

       X) Tarnished Plant Bug
             - adults and nymphs attack flower pistils of strawberries
             - causes deformed fruits; nubbins and berries with excessive apical seediness
             - serious problem; control as blossom buds become visible
             - as flowers start to open and when berries are half grown
             - don't spray during period of pollination

       Y) Slugs
             - serious problem in strawberries especially during wet periods, when mulched
             - or when allowed to become too thick; baits such as Deadline will help

       Z) Sunscald
             - more common in apples or pears
             - early spring sun warms southwest side of tree
             - sap starts to flow and low night temperatures damage cells; canker develops

     AA) Gumosis
             - exude from truck of stone fruits due to inner trunk damage


Todd Weinmann, Extension Horticulturist & Master Gardener Coordinator
Phone: (701) 241-5707
E-mail: todd.weinmann@ndsu.edu

Go to Fruit Growing Page

Go to Horticulture Page