Almond (Prunus amygdalus Batsch cv. Nonpareil), apricot (Prunus armeniaca L. cv. Royal Blenheim), and peach [Prunus persica (L.) Batsch cv. Halford] grafted nursery stock seedlings were exposed once per week for 4 hours to a maximum O3 concentration of 0.25 μl·liter-1 in field exposure chambers. Exposures were repeated for a total of 4 months in 1986 (year 1) and 1987 (year 2). Trunk caliper, number of shoots, and net growth (total seasonal weight increase) were measured at the end of each year. Almonds appeared to be the most sensitive to O3. Almond seedlings exhibited extensive foliar injury from O3, while apricot and peach seedlings were relatively insensitive. Total net growth of O3-exposed almond was reduced during both years relative to the controls and an impact on caliper was evident after year 2. Apricot seedlings exposed to O3 developed a thinner trunk but more shoots than the controls in both years. Peach tree seedlings exposed to O3 had fewer shoots than the controls at the conclusion of year 2 but thicker trunks after both years. No significant difference in variance or shape of distribution of net growth within the treatment populations between O3-exposed seedlings and controls was detected for any of the three fruit crops. The impact of O3 on young, nonbearing perennial fruit crops may be most evident in specific growth characteristics, such as net growth or trunk caliper.
Patrick M. McCool and Robert C. Musselman
Robert C. Musselman, Jerry L. Sterrett, and Victor Voth
Field plots of strawberry (Fragaria × ananassa Duch cv. Chandler) were exposed to two 1-hr nighttime simulated fog episodes per week at specific acidities from pH 1.6 to 3.2, or no fog. Small, distinct, irregularly shaped, rust-colored lesions developed on foliage and fruit after a single 1-hr exposure to acidic fog at low pH. Fog episodes at pH 1.6 resulted in death of the plants after 8 weeks. Strawberries tolerated short-term exposure to acidic fog at pH 2.0 or higher, with little or no negative effect on growth, yield, or fruit soluble solids. However, calyx injury from acidic fog reduced marketability at pH levels up to 2.8. ‘Douglas’, ‘Chandler’, ‘Selva’, ‘Parker’, and ‘Soque!’ differed in magnitude of response to acidic fog in greenhouse exposures.
Patrick M. McCool, Jerry L. Sterrett, and Robert C. Musselman
The portable fog canister apparatus, first described in HortScience [20(6): 1127–1129, December 1985], has been in use for about 3 years. It was recently discovered that older fog canisters in use for extended periods of time can possibly fail under pressure, resulting in separation of the top of the canister from the main body. Of more than 50 canisters constructed, only one canister has failed. Although canisters are soundly constructed, failures of the canisters can result in bodily harm or property damage. The tapped fittings appear to be the weak point of the canister design. If these fittings are stressed (e.g., an impact to the fitting), the PVC canister can be weakened. These canisters should be checked regularly for fractures surrounding any gas or water fittings. As with any system under pressure, weak points can fail suddenly and with significant force. It is recommended by us that the canisters be placed within some type of containment structure (group the canisters with a closed box) or users should otherwise modify the canisters so that sudden failures will be contained. Caution should always be exercised in the vicinity of the canisters when the system is pressurized.
Robert D. Shertz, W. J. Render, and R. C. Musselman
Three cultivars of greenhouse-grown apple trees (Malus domestica, Borkh.) were fumigated for single, 4-hour exposures with ozone (O3) and/or sulfur dioxide (SO2) at 0.40 and 0.80 ppm. Fumigations were performed in a plexiglass chamber situated within a controlled environment walk-in growth chamber. All 3 cultivars responded to treatments in a similar manner. When applied separately both gases induced characteristic foliar injury. In general, apple trees were more sensitive to 0.40 ppm O3 than to 0.40 ppm SO2; but they responded similarly to 0.80 ppm O3 or SO2. Foliar injury, leaf abscission, and shoot growth reduction were greatest when 0.80 ppm O3 and 0.80 ppm SO2 were combined. The data showed a less-than additive response when the 2 pollutants were combined; a response due, in part, to the high amount of injury induced by single pollutants at these concentrations. All O3 and/or SO2 fumigations resulted in stomatal closure.
Robert C. Musselman, Jerry L. Sterrett, and Andrew L. Granett
A portable fogging apparatus has been developed to deliver fog to field or greenhouse experimental plots. The device is inexpensive, easy to construct, requires little maintenance, and is transported easily to remote locations. The system uses compressed gas, but requires no pressurized fresh water source or electrical power. It has been used successfully to deliver acidic fogs both to remote field plots and to greenhouse plants.
Philip L. Forsline, Robert C. Musselman, Walter J. Kender, and R. J. Dee
Mature ‘McIntosh’, ‘Empire’, and ‘Golden Delicious’ apple trees (Malus domestica Borkh.) were sprayed with simulated acid rain solutions in the pH range of 2.5 to 5.5 at full bloom in 1980 and in 1981. In 1981, weekly sprays were applied at pH 2.75 and pH 3.25. Necrotic lesions developed on apple petals at pH 2.5 with slight injury appearing at pH 3.0 and pH 3.5. Apple foliage had no acid rain lesions at any of the pH levels tested. Pollen germination was reduced at pH 2.5 in ‘Empire’. Slight fruit set reduction at pH 2.5 was observed in ‘McIntosh’. The incidence of russetting on ‘Golden Delicious’ fruits was ameliorated by the presence of rain-exclusion chambers but was not affected by acid rain. With season-long sprays at pH 2.75, there was a slight delay in maturity and lower weight of ‘McIntosh’ apples. Even at the lowest pH levels no detrimental effects of simulated acid rain were found on apple tree productivity and fruit quality when measured as fruit set, seed number per fruit, and fruit size and appearance.