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Timothy Waller, Rutgers Cooperative Extension
(June 15, 2023)
Source: Rutgers Plant and Pest Advisory
Diseases on the radar
Phytophthora, Pythium, Phytopythium root diseases
Compounds used to control Oomycetes (Phytophthora, Pythium, Phytopythium) are called Oomycides and are fundamentally different than those used for fungal and bacterial diseases. Therefore, proper identification is required, as a plant with a fungal root rot (black root rot or rhizoctonia) would require completely different materials.
Contact the Rutgers Plant Diagnostic Lab for diagnostic services. Within available materials there are three main groups, which describe where they will work on the plant given the application technique. Cultural practices are always more important than materials, especially in this case. Management focuses around treating the roots, or providing materials that reach the roots.
Protectants – are non-mobile, meaning they stay exactly where applied, must be root / drench / wateredin, applied.
Xylem mobile systemics – move upwards, and the roots must be treated.
Translaminar systemics – move very short distances into tissues, again meaning the roots must be
targeted.
Amphimobile/Fully systemics (P07 / phosphonate group)– can move upwards to needles (xylem) and down to the roots (phloem) meaning foliage or roots can be targeted.
Refer to each label for treatment intervals as they vary greatly, however it is valuable to get ahead of this pathogen as very few materials can “cure” plants. Additionally, more than one material should be in your tool kit as Mefenoxam-resistance has been identified in the Mid-Atlantic region.
NOTE: Do not apply group P07 and copper-based fungicides within 14d of one another, as phytotoxicity
is likely to occur!
**Fenstop (Group 11) – Now approved for outdoor nurseries!
Leaf spot / foliage disease management
About: Most leaf spots are caused by several different genera of fungi, including but not limited to Alternaria, Colletotrichum, Cercospora, Diplocarpon, Phoma, Phyllosticta, and Septoria. There are also bacteria that can cause leaf spot (Psuedomonas and Xanthamonas) and even foliar nematodes (Aphelenchoides). Some common ornamental species that are regularly affected by leaf spot / foliage pathogens include maple, hydrangea, cherry, crape myrtle, redbud, viburnum, oak, Virginia sweetspire, and rose, though there are many other plants that can also be infected.
Cultural management: While the symptoms may not appear until later in the season, the infection period starts in the spring. Reducing the leaf wetness period by limiting overhead irrigation and increasing airflow can help to prevent these diseases, as well as proper sanitation by removing any diseased leaves from the area.
Material considerations: Protective fungicides and/or bactericides can also be effective if applied early in the season before the symptoms develop. Materials include copper hydroxide, mancozeb, propiconazole, chlorothalonil, myclobutanil, azoxystrobin, or thiophanate-methyl.
Boxwood Blight (BWB): If BWB is important to your business – Use the USPEST Boxwood Blight Risk Model (uspest.org/risk/boxwood_app).
Recent VIRUS observations:
Lilac Ring Mottle Virus – tentatively identified in multiple varieties of Syringa vulgaris in southern NJ. This would be a first-report in our state. Please closely inspect your Syringa for any viral symptoms. This virus is reported to spread mechanically (pruning, propagating, equipment). Please see this informative webpage about Lilac Ring Mottle Virus (PNW Pest Management Handbook)
If you suspect this virus in your Syringa PLEASE CONTACT – twaller@njaes.rutgers.edu– we would like to compile data to help reporting this in NJ – which will help our growers manage this virus.
Tobacco Rattle Virus – is suspected to be present in multiple hosts, especially Peony. Please be aware this virus has a huge list of host plants and is highly transmissible by plant sap (through pruning, damage, handling, root feeding (nematodes), etc.). Please see this informative webpage about Tobacco Rattle Virus (TRV) (Iowa State).
Nutrient Management
Managing Soluble Salts by Monitoring EC
(William Errickson, Rutgers Cooperative Extension)
It is important to monitor fertilizer and salt concentrations in ornamental plants to ensure that the plants are receiving adequate nutrients, while not allowing salts to build up and cause damage. There are various methods to monitor salt concentrations by measuring electroconductivity (EC) and seeing if that reading is within the optimum range for a particular plant species. Two common procedures for measuring EC include the saturated media or paste extract (SME) and the pour through (PT) method. Many university and commercial labs will use the SME method, as it has shown to be reliable and there have been numerous research studies and fertility trials used to develop general interpretation guidelines based on this procedure.
However, the process can be somewhat challenging to accurately execute outside of a laboratory setting.
The PT method was developed as simplified and practical way to reliably measure EC for container grown crops. Each method has its advantages in helping to maintain acceptable levels of soluble salts. Strategies to keep salt levels low include: (a) keep adequate moisture in the growing medium, (b) avoid applications of dry fertilizer or highly concentrated nutrient solutions to a dry growing medium, (c) avoid fertilizers that give a high salt stress for a given amount of nutrient (high salt index), and (d) be alert to changes in environmental conditions (like temperature and humidity) that affect plant transpiration, soil water evaporation, and nutrient release from slow or controlled-release fertilizers. For more information, see the fact sheet: Monitoring and Managing Soluble Salts in Ornamental Plant Production by Johnson and Cabrera.
Plant Tissue Analysis
Plant tissue analysis can provide you with valuable information about the current nutrient levels of your plants. It will let you know if your fertilizer applications are optimized, and it can help to identify any nutrient deficiencies or toxicities that may be present. A plant tissue analysis is a good way to check in on the fertility levels of your plants mid-season, especially if something just doesn’t seem right and you want to accurately diagnose the problem. When collecting your sample, it is important to collect leaves from multiple representative plants of the same species. This will help to improve the accuracy of the analysis. You will need approximately one pint of leaf material to send to the lab. The Agricultural Analytical Services Lab at Penn State University offers plant tissue analysis services that include 10 elements: nitrogen, phosphorus, potassium, calcium, magnesium, manganese, iron, copper, boron, and zinc. They also provide a report with fertility recommendations for the specific crop that was tested. The cost is approximately $24 per sample (plus shipping) depending on which type of tissue analysis you are looking for.
Native Plant Spotlight
American Holly (Ilex opaca) is a native tree species that is important in our coastal maritime forests. In the landscape, it can be used to create evergreen hedges with high deer resistance. It is moderately salt and drought tolerant, with blooms from May through June that attract bees and butterflies. American holly’s redberries persist through the winter months to feed birds and other wildlife. American holly branches can also be cut and harvested for holiday wreaths and other decorations.
Email: twaller@njaes.rutgers.edu. Phone: 856-451-2800 Ext. 1.