Diseases Associated with Juniperus Osteosperma and a Model for Predicting Their Occurrence with Environmental Site Factors

Volume 46 Number 3 Article 7

7-31-1986

Diseases associated with Juniperus osteosperma and a model for predicting their occurrence with environmental site factors

E. D. Bunderson Utah Technical College, Provo

D. J. Weber Brigham Young University

D. L. Nelson USDA Forest Service, Intermountain Research Station, Shrub Sciences Laboratory, Provo, Utah

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Recommended Citation Bunderson, E. D.; Weber, D. J.; and Nelson, D. L. (1986) "Diseases associated with Juniperus osteosperma and a model for predicting their occurrence with environmental site factors," Great Basin Naturalist: Vol. 46 : No. 3 , Article 7. Available at: https://scholarsarchive.byu.edu/gbn/vol46/iss3/7

This Article is brought to you for free and open access by the Western North American Naturalist Publications at BYU ScholarsArchive. It has been accepted for inclusion in Great Basin Naturalist by an authorized editor of BYU ScholarsArchive. For more information, please contact [email protected], [email protected]. DISEASES ASSOCIATED WITH JUNIPERUS OSTEOSPERMA AND A MODEL FOR PREDICTING THEIR OCCURRENCE WITH ENVIRONMENTAL SITE FACTORS

E. D. Bunderson', D. J. \Vel)er-, and D. L. Nelson'

Abstract. —On 17 Utah juniper (Juniperus ostcospcrvia [Torrey] L.) sites studied in Utah, Gymnosporangium inccmspicuum was the most common rust fungus, followed in frequency and severity by G. nelsoni , G. kernianum , and

G. speciosiim . The incidence of G. kernianum was correlated with moderate temperatures and greater than average precipitation. True mistletoe, Phoradendron juniperimnn Engelm., was present on seven sites. Incidence of foliage diseases of the mold-mildew type was low on sites with low spring and summer temperatures and high on sites with high summer and fall precipitation. Wood rot was common, and incidence seemed to be correlated with low winter temperatures and low soil nitrate but not with annual precipitation. Needle blight, shoot dieback, and needle cast symptoms were common and considered of abiotic origin. Their nonparasitic nature was indicated by lack of association with pathogenic organisms and the positive correlation of their incidence with winter injury and summer drought factors. Needle blight was also positively correlated with high soil salinity but negatively with high soil calcium regardless of salinity. A nonparametric model was developed that accurately predicted the frequency of the mold-mildew type diseases of

/. osteospcnna based on measured environmental site factors.

The pinyon-juniper woodland is a wide- spread vegetation type in the southwestern United States, estimated to cover from 30 to 40 milhon hectares (Allred 1964). Histori- cally, pinyon-juniper woodland vegetation has provided numerous benefits including fuel, building materials, charcoal, nuts, Christmas trees, medicines, etc. (Tueller et al. 1979, Hurst 1977, Lanner 1975, Cronquist et al. 1972, Callegos 1977). About 80% of the total acreage is grazed, contributing signifi- cantly to the available forage for livestock and wildlife (Clary 1975), and pinyon-juniper woodlands are becoming increasingly valued for their watershed, aesthetic, and recre- ational values (Giffbrd and Busby 1975).

This ecosystem is a large component of the vegetation of Utah (62,705 km' or 28.6%,

Kuchler 1964), and it has the potential to add substantially to the economic and aesthetic activity of the state. Despite this potential, little research has been done to explore the physiological relationships and autecology of Fig. 1. Location of 17 study sites in Utah. this vegetation type. Many complex environmental factors con- water, nutrients, oxygen, and carbon dioxide tribute to the variety of interactions in a interact with "site quality" or "condition" fac- pinyon-juniper ecosystem. Consumable "sup- tors such as temperature and precipitation ply factors" of the environment such as light. (Harper 1977). The effects of species density,

'Utah Technical College, Provo, Utah 84604 -Department of Botany and Range Science. Brigham Young Uni\ersity, Pro\o, Utah 84602. ^USDA Forest Service, Intermountain Research Station, Shrub Sciences Laboratory, Provo, Utah 84601.

427 ) .

428 Great Basin Naturalist Vol. 46, No. 3

Table 1. Description of symptoms and assessment methods for diseases of Juniper osteosperma

Diseases of y. osteosperma Iniurv symptom or sign Rating scale

Needle blight Senescent or decadent foliage or twigs. Terminals Percent of the total plant affected may show yellow or red-brown coloration. May or may not show evidence of fungal fruiting bodies.

Needle cast Bare twig terminals from which foliage scale leaves Percent of the total plant affected have fallen (twig terminals of living branches).

Tip dieback Senescent or decadent foliage or twig terminals Percent of the total plant affected showing brown to grey coloration. May or may not show evidence of fungal fruiting bodies.

Pathogen

Gymnosporangium rusts:

G. inconspicuum Presence of follicolous or caulicolous telia having Rated as light, moderate, or cartiform pedicels accompanied by little or no heavy: a) light: 1-3 telial infect-

fasciation of branches. tions in a 2 ft breast high circum- ference section of tree, b) moderate: 4-10 telial infections in equivalent area, c) heavy: more than 10 telial infections in equivalent area.

G. nelsoni Presence of galls with irregularly compressed, Actual or estimated number of wedge-shaped telia; on twigs or branches. galls per tree.

G. kerniamim Presence of well-defined or modified witch's brooms Actual or estimated number of (branch fasciation) with foliicolous, bluntly conical witch's brooms per tree. telia.

G. speciosum Presence of cristiform or crenate telia on fusiform Actual or estimated number of swellings. fusiform swellings per tree.

Wood rot fungi (i.e., Presence of heart rot or decayed areas in trunk or Presence rated as light, moder- Fames jttniperinum branches. Fungal fruiting bodies may or may not ate, or heavy. be present.

Mold and/or mildew Fungal mycelial growth on foliage. Presence rated as light, moder- (unidentified spp.) ate, or heavy.

Mistletoe (Phoradendron Presence of viable mistletoe foliage in tree. Actual or estimated number of juniperinum) growth areas per tree.

habitable niches, pathogens, seasonality, and 1974). Several studies have treated disease roles of predators such as grazing animals in- and/or insect factors of pinyon pines (McCam- fluence the diversity and stability of pinyon- bridge and Pierce 1974, McGregor and San- juniper woodlands, as do naturally occurring drin 1968, Hepting 1921), but little research catastrophic events (i.e., fire) or deliberate in these particular areas has dealt with ju- manipulation or intervention by man. niper. The ecological dynamics of the pinyon- The objectives of this study were to survey juniper ecosystem have been studied by Pear- the diseases of Utah juniper (Juniperus os- son (1920), Woodbury (1947), Daniel et al. tcospenna [Torrey] L.), particularly those in- (1966), and Vasek (1966) and typically have duced by fungi, and to relate their occur- been oriented toward range and resource rence, frequency, and severity to selected management. Synecological studies of environmental factors in several pinyon- pinyon-juniper have included work in latitu- juniper habitats throughout Utah. dinal and elevational patterns (Daubenmire interactions with understory vegeta- 1943), M.\TERIALS AND METHODS tion (West et al. 1975), paleoecological influ- ences (Cottam 1959), and climatic and Seventeen representative pinyon-juniper edaphic relationships (Beeson 1974, Hunt sites in Utah were studied from April to Octo- July 1986 BUNDERSON ET AL. : JUNIPER DISEASES 429

Table 2. Location of 17 primary juniper study sites in Utah.

Site no. Weather station

Jat kson Springs St. George Tobin Bench Veyo Power House Peters Point Monticello Alkah Ridge Blanding C\ clone Flat Natural Bridges Natl. Mon. Indian Peak Desert Expt. Range Ephraim Ephraim Sorensens Fid. Manti Manti Black Mountain Salina Triangle Mountain Salina Beaver Ridge Beaver Ciordon Creek Hiawatha Dutch John Flaming Gorge Taylor Flat Allen's Ranch Rabbit Gulch Hannah Henry Mountains (Stevens Narrows) Capitol Reef Natl. Park Henry Mountains (Airplane Flat) Boulder

ter method (Phillips 1959). Each tree was measured for height, stem diameter, and age and then assessed for signs and symptoms of disease. Diseases were classed in three causal categories: (a) rust fungi {Gymnosporangium spp.), (b) miscellaneous fungus diseases (e.g.,

tip burn, die back, stem decay), and (c) para- sitic higher plants. Nonparasitic injury was also assessed. Descriptions of diseases, pathogenic agents, and assessment methods are

found in Table 1. The percentage of deca- dence for each tree was estimated and an

overall vigor score (1 = good, 2 = moderate, 3 ^ poor) was assigned to each tree. Since some areas of the state were not rep-

resented in our 17 primary sites (Table 3), we added 15 additional sites (Fig. 2) in which just

the incidence o{' Gymnosporangium rusts was studied. We used the standard U.S. Forest Service ratings as listed in the addendum to Table 4. Since each site had its own pattern of infec-

Fig. 2. Observations of four Gymnosporan^ium spe- tion, we calculated severity indexes to reflect cies in selected Utah sites. both the total number of trees infected with each causal agent and the severity of that in-

ber 1982 (Fig. 1). Sites were .selected for cli- fection on each tree (Table 2). max pinyon-juniper vegetation and minimal We measured concentrations of several soil structural disturbance by people, although mineral nutrients (N, P, K, Ca, Mg, Na, Fe, most sites had a long history of grazing by SO4) and other soil properties (pH, EC, sand, domestic animals and wildlife. Soils were pri- silt, clay) by digging five soil pits along each marily derived from marine shales, conglom- transect and pooling samples from the top 12 erates, siltstones, and sandstones (Bunderson inches of soil from each pit. Soils were acid

et al. 1985). digested and analyzed for mineral content us- Transects at each site consisted of 96 Utah ing a Technicon II Auto Analyzer and atomic juniper trees randomly selected by the quar- absorption spectroscopy. Temperature and 430 Great Basin Naturalist Vol. 46, No. 3

Table 3. Observations of three Gijmnosporangium species in selected Utah sites. .

July 1986 BuNDERSONETAL: Juniper Diseases 431

Table 4. Description of rating system for diseases ol Juniper ostcospenna

Infection level = Number of trees infected with pathogen.

Severity

a. G. inconspiciium = Average rating of infections per tree = No infection 1 = Light infection 2 = Medium infection 3 = Heavy infection

b. G. nelsoni = Average number of galls/tree

c. G. kernianum = Average number of witch's broom/tree

Severity Index a. G. inconspiciium = Proportion of infected trees (expressed as a %) ^ ,qq

Site rating 3

b. G. nelsoni = Severity

Average number galls/meter proportions of infected trees (%)

c. G. kernianum =- Severity

Average height of trees at site proportions of infected trees (%)

Mold mildew Severity = Percentage of trees infected; Severity index = Proportion (%) x percentage infected (severity)

Wood- rotting fu ngi Severity = Sum of percentage of trees infected with trunk, branch, twig rot; Severity index = Proportion (%) X severity

Mistletoe Severity = Average number of broom/tree; severity index =^ Proportion (%) x severity

'Needle blight Severity = Average percentage of infection/infected tree; Severity index ^ Proportion (%) x severity

Needle cast

Severity = Average percentage of mildew on all infected trees (cumulative); Severity index = Proportion (%) x severity

Tip dieback Severity = Average percentage of infection/infected tree; Severity index = Proportion (%) x severity

G. nelsoni was much more variable thau that temperatures and a greater than average an- ofG. inconspiciium. nual precipitation, particularly during the

We found Gymnosporangiuni kernianum summer (Tables 5, 6). Bethel on fewer sites than either G. incon- We found a fourth species, Gymnospo- spicuu7n or G. nelsoni. This species stimu- rangiuyn speciosimi , on only one primsiry site lates shoot fasciations (witch's brooms) on (Site 12) and one supplementary site (Sego). It which foliicolous telia are formed. Numbers of forms bright orange cristiform or crenate telia brooms per infected tree ranged from to 23 on fusiform stem swellings, with loose fascica- and size of brooms from 3 to 130 cm in diame- tions usually associated with the infected area, ter. The incidence of G. kernianum was con- Variation in host susceptibility complicates siderably less than that of either G. incon- establishing cause and effect relationships spicuum or G. nelsoni. As with G. incon- with physical environmental factors for G[/m- spicuum, only active infections were re- no.sporangium rusts. Differences in resistance corded. to cedar-apple rust have been known for many Correlations between temperature and years (Moore 1940) as well as differences in precipitation in our research sites indicate pathogenicity of the rust (Aldwinkle 1975). It

that G. kernianum is favored by moderate has been suggested that the genetic variability 432 Great Basin Naturalist Vol. 46, No. 3

Gymnosporangium inconspicuun

80 +

S, 70

III 2 3 4 5 6 7 8 9 1011 12 13 1415 16 17

90 July 1986 BuNDERSON ETAL: Juniper Diseases 433

Table 5. Correlations between/, osteosperma diseases and insects and temperature in the different time quarters

(Q).

Pathogen 434 Great Basin Naturalist Vol. 46, No. 3

Wood Rolling Fungi Wood Rotting Fungi

2 3 4 5 6 7 12 13 14 15 16 17 LjLIi Ml 5 6 7 8 9 101112 13 14 15 1517

Mold Mildew

2 3 4 5 6 7 8 9 101112 1314 151617

90 July 1986 BUNDERSON ET AL.; JUNIPER DISEASES 435 436 Great Basin Naturalist Vol. 46, No. 3

Table 7. Correlations between/, osteosperma diseases and insects versus soil variables.

Pathogens July 1986 BuNDERSON ETAL: Juniper Diseases 437

ppni Mg 438 Great Basin Naturalist Vol. 46, No. 3

Table 8. Correlations between/, osteospcnna diseases and insects and site characteristics. ulv 1986 BUNDERSON ET AL. : JUNIPER DISEASES 439 440 Great Basin Naturalist Vol. 46, No. 3

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