during the summer. Being a warm-season grass, it was also dormant in the winter, ir- respective of irrigation regimes. Neverthe- less, its spring and fall growth allowed it to persist and compete with all invading spe- cies. Time of year We collected data in May, July, and De- cember to target plant responses at critical times. May readings reflected the response to the winter and early spring months; July readings, response under high tempera- tures; and December readings, response during the winter, which identified dor- mancy of warm-season species. Figure 2 presents responses of four spe- cies, withquite different growthpatterns, to the three irrigation regimes and three times of year. Santa Ana bermudagrass showed Russian wheat (green ) and birdcherry oat aphid. little difference in performance among the three irrigation regimes in May and July. In December, there was a downward trend in performance, reflecting the growth cessa- tion and approaching winter dormancy of Suction trap reveals 60 wheat this warm-season turfgrass. Conversely, the growth pattern of Sirosa phalaris showed its summer dormancy aphid species, including with higher cover and quality ratings before (May) and after (December)dormancy. Buffalograss performed similarly at all Russian wheat aphid irrigation regimes. It clearly showed the dormancy pattern that characterizes the Keith S. Pike o David Allison a Leslie Boydston o Calvin 0. Qualset species during summer and winter months, despite the irrigation regime. Herbert E. Vogt D Charles G. Summers Glaucus saltbush showed less of a sea- sonal response than an irrigation response. This species performed better as a turf cover Effective aphid management such as lady beetles and syrphids, has not when irrigated at the2070 regime than at the strategies depend on a knowledge been practical in large-scale crop produc- 40 and 60% regimes. tion, but the natural occurrence of these of the economically important spe- and fungal diseases or parasites has Conclusions cies present in an area and their reduced aphid populations in such crops as Of the 27 turfgrasses and ground covers flight behavior. A suction trap at sugarbeets. Adjusting planting dates to tested in this study, bermudagrasses and UC Davis collected 60 aphid spe- avoid a damaging infestation can be effec- seashore Paspalum were the best perform- cies, most of which are economi- tive in barley, wheat, sugarbeets, and some ing turfgrasses under very low irrigation other crops. Control by insecticidesis effec- regimes. Two species of saltbush, buffalo- cally important. The trap detected tive, but is costly when repeated applica- grass, and two varieties of Phalaris also gave the first specimens of the Russian tions are needed. Insecticides usually do comparatively good cover and quality. wheat aphid found in northern not control diseases caused by aphid-trans- This work showed that there are existing California. mitted viruses, because the viruses are turfgrasses, and other plant material main- transmitted from the aphid to the plant tained as turf, that are capable of surviving during a short feeding period before the and giving cover under extremely low irri- occur throughout the world on a insecticide kills the aphid. gation regimes. These materials apparently wide variety of cultivated and wild plants. resist thestress of low water application by Many aphids cause economic damage Trapping aphids various mechanisms, including dormancy, through direct feeding, injection of toxins, Monitoring aphid populations is a first deep roots, and low rates of water use. transmission of plant pathogenic viruses, step in developing crop management prac- contamination with honeydew, or their tices to minimize losses. Methods of deter- VictorA. Gibeault is Extension Environmental presence on edible plant parts. They may mining the aphid species and numbers Horticulturist, Department ofBotanyand Plant attack any portion of the plant including present include ground-leveI collection of Sciences;JewellL. Meyer is Extension Irrigation leaves, stems, fruit, and roots. flying aphids in pan traps, vacuum or and Soils Specialist, Department of Soil and Because aphids have adverse effects on sweeping techniques to remove aphids di- Environmen tal Sciences;and Richard Au tio and many crops, are widely distributed, and rectly from plants, and direct counts of in- Ralph Strohman are Staff Research Associates. reproduce rapidly, aphid control has been sects on plants. Aphids can also be collected A11 are with the University of California,River- under investigation for many years. The at various distances above the soil surface side. introduction of biological control agents, with suction traps. In the western United

22 CALIFORNIA AGRICULTURE, VOLUME43, NUMBER 6 States and in Europe, suction traps 28 feet late 1988. California’s first trap was placed above the surface have been effective in at the Agronomy Farm on the University of assessing seasonal aphid flights and in de- California Davis campus in 1987. termining aphid numbers, which can be The results of the first year of monitoring related to potential crop losses. None of aphid speciesfrom the Davis trap presented these methods alone is sufficientto establish here demonstrate the variety of aphid spe- management decisions. cies detected and their seasonal flight distri- A network of more than 75 aphid suction butions. A sample was taken from the trap traps established through the Western each week from February through Novem- Region Integrated Pest Management proj- ber 1988 and assayed at the aphid labora- ect and various state agricultural experi- tory at Prosser, Washington. The trap has ment stations is now being used in the west- already been useful in detecting the Russian ern United States and Canada. The suction wheat aphid for the first time in northern trap was developed at the Washington State California. University Irrigated Agriculture Research and Extension Center. It has proved useful Aphid species found in 1988 in detecting which aphid species were More than 60 species representing 37 prevalent as vectors of the barley yellow genera were trapped, of which about 80% dwarf virus, a generally distributed patho- are economically important. The 10 most gen of small grains. abundant species were birdcherry oat The traps have also been used to track the aphid (with43.4%of total catch), pea aphid, advance and the spring, summer, and fall green peach aphid, turnip aphid, migrations of the Russian wheat aphid, aphid, greenbug, rice root aphid, mealy Diclruphis noxfu,a new pest first found in the plum aphid, rose grass aphid, and green United States in 1986. Because of the need citrus aphid (fig. 1, table 1). for information on economicallyimportant In the United States, 27 aphid species are Aphid suction trap is part of the network of traps the system Of traps has been ex- capable of colonizing and feeding on small established in the western states. panded annually, most recently in Califor- grains; at Davis, 12 cereal aphid species nia, where seven new traps were installed in were detected. The predominant one was

I TABLE 1. Winged cereal aphids, other economic aphids, and noneconomic aphids sampled by suction trap, Davis, California, February through November 1988 .PPrcent -. .. of.- . . No. of aphids trapped Total Cereal aphid aphid Scientific name Common name Feb Mar Apr May Jun Jul Aug Sep Oct Nov Total catch catch CEREAL APHIDS Aphis arrnoraciae Western aster root aphid 0 0 1 100001 0 3 <1 0 01 Anoecia corm Dogwood aphid 0 0 0 000001 0 1 <1 0

ALL ECONOMIC APHIDS Subtotal 427 2730 1705 246 175 35 46 109 330 337 6140 80 8 -

NONECONOMIC APHIDS Subtotal 4 307 469 237 128 116 11 72 47 68 1459 19 2 -

ALL APHIDS TOTAL 431 3037 2174 483 303 151 57 181 377 405 7599

CALIFORNIA AGRICULTURE, NOVEMBER-DECEMBER 1989 23 The cream-colored stripes on wheat leaves are during the winter and spring growing sea- the most characteristic symptom of damage by sons. Russian wheat aphid. Leaves later curl in a The suction trap results indicated a very corkscrew fashion and resemble onion leaves. low frequency of winged Russian wheat birdcherry oat aphid, a common aphid pest aphids during May-July. It was not known and virus vector of worldwide distribution. how or if these aphids would survive In Washington state, this species is abun- through the summer in California. None dant during the fall, sometimesconstituting were collected during the fall. However, in up to 95% of the flying aphids, but in the September-planted wheat, barley, and oats warmer climate of California, its peak at Davis, typical symptoms of Russian flights occurred between February and wheat aphid feeding were observed in April. Six of the 12 species of cereal aphids November. Specimens were positively trapped at Davis form colonies on the roots identified later as Russian wheat aphid. of wheat and other plants: western aster This was a mixed planting of Atlas 57 bar- root aphid, dogwood aphid, Colopha ulmi- ley, Tanori 71 wheat, and California Red oat cola, apple grain aphid, rice root aphid, and varieties. In January 1989, counts were elm grass root aphid). These are probably made of healthy and affected plants from minor pests in California, except possibly three replicates of this planting. Barley was rice root aphid. The remaining six species the most severely affected (71 of 134 plants, are potentially major pests, depending on or 53%),followed by wheat with 13 of 50 their abundance and the percentage trans- plants (26%)showing symptoms induced mitting virus. Previous work by V. Burton by Russian wheat aphid. Oat was practi- and others in California has shown that cally free of damage (2 of 182 plants, 1%). birdcherry oat aphid, English grain aphid, The appearance of Russian wheat aphid rose grass aphid, and greenbug are the most in the suction trap earlier in the year was important species, in that order. taken as a warning that this pest might The pattern or peak flight period of most appear in the next crop cycle. This was the economic aphid species at Davis occurred case, since a low level of Russian wheat during the first half of the year in contrast to aphid infestation was documented at the regions further north. Three exceptions UC Davis Agronomy Farm in November were potato aphid, which peaked in June, 1988. No winged individuals were found at July, and August; and pea aphid and green that time on either the grain or in the trap. peach aphid, which peaked in April and This result emphasizes the need for regular also in October and November. field scouting as well as monitoring suction traps to develop crop management infor- Grain aphids Green peach aphid - Rhopalosiphum padi Birdcherry oat mation needed to reduce losses from --- R. rufiabdominalis Rice root aphid The presence of green peach aphid in aphids. These observations and the rapid ..... Schizaphis graminum Greenbug dirhodum Rose grass aphid suction trap catches in the spring or summer spread of Russian wheat aphid across the is important, even in low numbers, because western United States as well as a similarly of its potential to transmit virus to crops. rapid dispersion in South Africa, point to Host crops include almond, , carna- the importance of monitoring aphid distri- tion, peach, pepper, potato, spinach. straw- bution throughout California to develop berry, sugarbeet, , turnip, and appropriate control strategies. wheat. Sugarbeet yellows and potato leaf- roll viruses are among important viruses Conclusions To three01 er transmitted by this aphid. In the first year of use in California, the ecgnornic apiids suction trap provided an additional method - - Myzus persicae Green peach aphid Russian wheat aphid 4 lo'wo 1 - - Acyrthoslphon pisum Pea aphid of monitoring aphid species and their lwo ..... euphorbiae Potato aphid The Russian wheat aphid was first sighted flights. The results of the first year illustrate in Mexico in 1980 and in Texas in 1986. By the value of noting low frequencies of previ- 1988 it was found in 15 western and mid- ously undetected species, such as Russian western states. Crop losses were estimated wheat aphid. Because so many California at about $80 million in 1988. crops are affected by aphids, the expanded In California, the Russian wheat aphid network of suction traps and increased was first found in Imperial County in March ground-level scouting are highly recom- Next three other economic aphids 1988. Its discovery in Davis by suction trap mended. 1o.m - Lipaphis erysimi Turnip aphid - - Hyalopterus pruni Mealy piurn aphid in May 1988 was significant, since the spe- .__..Aphis citricola Green citrus aphid cies was not previously known north of Keith S. Pike is Entomologist,and David Allison Imperial County. In addition to Imperial and Leslie Boydston are Research Technicians, and Yo10 counties infested in 1988, the Rus- Irrigated Agriculture Research and Extension sian wheat aphid has been reported in 1989 Center, Washington State University, Prosser; in Alameda, Contra Costa, Fresno, Kern, Calvin 0.Qualset is Professor, and Herbert E. Los Angeles, Riverside, Sacramento, San Vogt is StaffResearch Associate, Department of Feb Mar Apr May Jun Jui Aug Sep Oct NOV Benito, San Bernardino, San Joaquin, Santa Agronomy and Range Science, University of Clara, and Solano counties. Because of this California, Davis;Charles G. Summers is Asso- Fig. 1. Seasonal distribution of 10 aphid spe- aphids prolific nature and its high potential ciate Entomologist, Department of Eiztomologi- cies caught most frequently in a suction trap at to damage wheat and barley, early detec- cal Sciences, UC Berkeley (stationed at UC Davis, California, 1988. tion and timely controls will be important Kearney Agricultural Center, Purlieu).

24 CALIFORNIA AGRICULTURE, VOLUME 43, NUMBER 6